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diff --git a/Documentation/x86/resctrl_ui.txt b/Documentation/x86/resctrl_ui.txt deleted file mode 100644 index c1f95b59e14d..000000000000 --- a/Documentation/x86/resctrl_ui.txt +++ /dev/null @@ -1,1121 +0,0 @@ -User Interface for Resource Control feature - -Intel refers to this feature as Intel Resource Director Technology(Intel(R) RDT). -AMD refers to this feature as AMD Platform Quality of Service(AMD QoS). - -Copyright (C) 2016 Intel Corporation - -Fenghua Yu <fenghua.yu@intel.com> -Tony Luck <tony.luck@intel.com> -Vikas Shivappa <vikas.shivappa@intel.com> - -This feature is enabled by the CONFIG_X86_CPU_RESCTRL and the x86 /proc/cpuinfo -flag bits: -RDT (Resource Director Technology) Allocation - "rdt_a" -CAT (Cache Allocation Technology) - "cat_l3", "cat_l2" -CDP (Code and Data Prioritization ) - "cdp_l3", "cdp_l2" -CQM (Cache QoS Monitoring) - "cqm_llc", "cqm_occup_llc" -MBM (Memory Bandwidth Monitoring) - "cqm_mbm_total", "cqm_mbm_local" -MBA (Memory Bandwidth Allocation) - "mba" - -To use the feature mount the file system: - - # mount -t resctrl resctrl [-o cdp[,cdpl2][,mba_MBps]] /sys/fs/resctrl - -mount options are: - -"cdp": Enable code/data prioritization in L3 cache allocations. -"cdpl2": Enable code/data prioritization in L2 cache allocations. -"mba_MBps": Enable the MBA Software Controller(mba_sc) to specify MBA - bandwidth in MBps - -L2 and L3 CDP are controlled seperately. - -RDT features are orthogonal. A particular system may support only -monitoring, only control, or both monitoring and control. Cache -pseudo-locking is a unique way of using cache control to "pin" or -"lock" data in the cache. Details can be found in -"Cache Pseudo-Locking". - - -The mount succeeds if either of allocation or monitoring is present, but -only those files and directories supported by the system will be created. -For more details on the behavior of the interface during monitoring -and allocation, see the "Resource alloc and monitor groups" section. - -Info directory --------------- - -The 'info' directory contains information about the enabled -resources. Each resource has its own subdirectory. The subdirectory -names reflect the resource names. - -Each subdirectory contains the following files with respect to -allocation: - -Cache resource(L3/L2) subdirectory contains the following files -related to allocation: - -"num_closids": The number of CLOSIDs which are valid for this - resource. The kernel uses the smallest number of - CLOSIDs of all enabled resources as limit. - -"cbm_mask": The bitmask which is valid for this resource. - This mask is equivalent to 100%. - -"min_cbm_bits": The minimum number of consecutive bits which - must be set when writing a mask. - -"shareable_bits": Bitmask of shareable resource with other executing - entities (e.g. I/O). User can use this when - setting up exclusive cache partitions. Note that - some platforms support devices that have their - own settings for cache use which can over-ride - these bits. -"bit_usage": Annotated capacity bitmasks showing how all - instances of the resource are used. The legend is: - "0" - Corresponding region is unused. When the system's - resources have been allocated and a "0" is found - in "bit_usage" it is a sign that resources are - wasted. - "H" - Corresponding region is used by hardware only - but available for software use. If a resource - has bits set in "shareable_bits" but not all - of these bits appear in the resource groups' - schematas then the bits appearing in - "shareable_bits" but no resource group will - be marked as "H". - "X" - Corresponding region is available for sharing and - used by hardware and software. These are the - bits that appear in "shareable_bits" as - well as a resource group's allocation. - "S" - Corresponding region is used by software - and available for sharing. - "E" - Corresponding region is used exclusively by - one resource group. No sharing allowed. - "P" - Corresponding region is pseudo-locked. No - sharing allowed. - -Memory bandwitdh(MB) subdirectory contains the following files -with respect to allocation: - -"min_bandwidth": The minimum memory bandwidth percentage which - user can request. - -"bandwidth_gran": The granularity in which the memory bandwidth - percentage is allocated. The allocated - b/w percentage is rounded off to the next - control step available on the hardware. The - available bandwidth control steps are: - min_bandwidth + N * bandwidth_gran. - -"delay_linear": Indicates if the delay scale is linear or - non-linear. This field is purely informational - only. - -If RDT monitoring is available there will be an "L3_MON" directory -with the following files: - -"num_rmids": The number of RMIDs available. This is the - upper bound for how many "CTRL_MON" + "MON" - groups can be created. - -"mon_features": Lists the monitoring events if - monitoring is enabled for the resource. - -"max_threshold_occupancy": - Read/write file provides the largest value (in - bytes) at which a previously used LLC_occupancy - counter can be considered for re-use. - -Finally, in the top level of the "info" directory there is a file -named "last_cmd_status". This is reset with every "command" issued -via the file system (making new directories or writing to any of the -control files). If the command was successful, it will read as "ok". -If the command failed, it will provide more information that can be -conveyed in the error returns from file operations. E.g. - - # echo L3:0=f7 > schemata - bash: echo: write error: Invalid argument - # cat info/last_cmd_status - mask f7 has non-consecutive 1-bits - -Resource alloc and monitor groups ---------------------------------- - -Resource groups are represented as directories in the resctrl file -system. The default group is the root directory which, immediately -after mounting, owns all the tasks and cpus in the system and can make -full use of all resources. - -On a system with RDT control features additional directories can be -created in the root directory that specify different amounts of each -resource (see "schemata" below). The root and these additional top level -directories are referred to as "CTRL_MON" groups below. - -On a system with RDT monitoring the root directory and other top level -directories contain a directory named "mon_groups" in which additional -directories can be created to monitor subsets of tasks in the CTRL_MON -group that is their ancestor. These are called "MON" groups in the rest -of this document. - -Removing a directory will move all tasks and cpus owned by the group it -represents to the parent. Removing one of the created CTRL_MON groups -will automatically remove all MON groups below it. - -All groups contain the following files: - -"tasks": - Reading this file shows the list of all tasks that belong to - this group. Writing a task id to the file will add a task to the - group. If the group is a CTRL_MON group the task is removed from - whichever previous CTRL_MON group owned the task and also from - any MON group that owned the task. If the group is a MON group, - then the task must already belong to the CTRL_MON parent of this - group. The task is removed from any previous MON group. - - -"cpus": - Reading this file shows a bitmask of the logical CPUs owned by - this group. Writing a mask to this file will add and remove - CPUs to/from this group. As with the tasks file a hierarchy is - maintained where MON groups may only include CPUs owned by the - parent CTRL_MON group. - When the resouce group is in pseudo-locked mode this file will - only be readable, reflecting the CPUs associated with the - pseudo-locked region. - - -"cpus_list": - Just like "cpus", only using ranges of CPUs instead of bitmasks. - - -When control is enabled all CTRL_MON groups will also contain: - -"schemata": - A list of all the resources available to this group. - Each resource has its own line and format - see below for details. - -"size": - Mirrors the display of the "schemata" file to display the size in - bytes of each allocation instead of the bits representing the - allocation. - -"mode": - The "mode" of the resource group dictates the sharing of its - allocations. A "shareable" resource group allows sharing of its - allocations while an "exclusive" resource group does not. A - cache pseudo-locked region is created by first writing - "pseudo-locksetup" to the "mode" file before writing the cache - pseudo-locked region's schemata to the resource group's "schemata" - file. On successful pseudo-locked region creation the mode will - automatically change to "pseudo-locked". - -When monitoring is enabled all MON groups will also contain: - -"mon_data": - This contains a set of files organized by L3 domain and by - RDT event. E.g. on a system with two L3 domains there will - be subdirectories "mon_L3_00" and "mon_L3_01". Each of these - directories have one file per event (e.g. "llc_occupancy", - "mbm_total_bytes", and "mbm_local_bytes"). In a MON group these - files provide a read out of the current value of the event for - all tasks in the group. In CTRL_MON groups these files provide - the sum for all tasks in the CTRL_MON group and all tasks in - MON groups. Please see example section for more details on usage. - -Resource allocation rules -------------------------- -When a task is running the following rules define which resources are -available to it: - -1) If the task is a member of a non-default group, then the schemata - for that group is used. - -2) Else if the task belongs to the default group, but is running on a - CPU that is assigned to some specific group, then the schemata for the - CPU's group is used. - -3) Otherwise the schemata for the default group is used. - -Resource monitoring rules -------------------------- -1) If a task is a member of a MON group, or non-default CTRL_MON group - then RDT events for the task will be reported in that group. - -2) If a task is a member of the default CTRL_MON group, but is running - on a CPU that is assigned to some specific group, then the RDT events - for the task will be reported in that group. - -3) Otherwise RDT events for the task will be reported in the root level - "mon_data" group. - - -Notes on cache occupancy monitoring and control ------------------------------------------------ -When moving a task from one group to another you should remember that -this only affects *new* cache allocations by the task. E.g. you may have -a task in a monitor group showing 3 MB of cache occupancy. If you move -to a new group and immediately check the occupancy of the old and new -groups you will likely see that the old group is still showing 3 MB and -the new group zero. When the task accesses locations still in cache from -before the move, the h/w does not update any counters. On a busy system -you will likely see the occupancy in the old group go down as cache lines -are evicted and re-used while the occupancy in the new group rises as -the task accesses memory and loads into the cache are counted based on -membership in the new group. - -The same applies to cache allocation control. Moving a task to a group -with a smaller cache partition will not evict any cache lines. The -process may continue to use them from the old partition. - -Hardware uses CLOSid(Class of service ID) and an RMID(Resource monitoring ID) -to identify a control group and a monitoring group respectively. Each of -the resource groups are mapped to these IDs based on the kind of group. The -number of CLOSid and RMID are limited by the hardware and hence the creation of -a "CTRL_MON" directory may fail if we run out of either CLOSID or RMID -and creation of "MON" group may fail if we run out of RMIDs. - -max_threshold_occupancy - generic concepts ------------------------------------------- - -Note that an RMID once freed may not be immediately available for use as -the RMID is still tagged the cache lines of the previous user of RMID. -Hence such RMIDs are placed on limbo list and checked back if the cache -occupancy has gone down. If there is a time when system has a lot of -limbo RMIDs but which are not ready to be used, user may see an -EBUSY -during mkdir. - -max_threshold_occupancy is a user configurable value to determine the -occupancy at which an RMID can be freed. - -Schemata files - general concepts ---------------------------------- -Each line in the file describes one resource. The line starts with -the name of the resource, followed by specific values to be applied -in each of the instances of that resource on the system. - -Cache IDs ---------- -On current generation systems there is one L3 cache per socket and L2 -caches are generally just shared by the hyperthreads on a core, but this -isn't an architectural requirement. We could have multiple separate L3 -caches on a socket, multiple cores could share an L2 cache. So instead -of using "socket" or "core" to define the set of logical cpus sharing -a resource we use a "Cache ID". At a given cache level this will be a -unique number across the whole system (but it isn't guaranteed to be a -contiguous sequence, there may be gaps). To find the ID for each logical -CPU look in /sys/devices/system/cpu/cpu*/cache/index*/id - -Cache Bit Masks (CBM) ---------------------- -For cache resources we describe the portion of the cache that is available -for allocation using a bitmask. The maximum value of the mask is defined -by each cpu model (and may be different for different cache levels). It -is found using CPUID, but is also provided in the "info" directory of -the resctrl file system in "info/{resource}/cbm_mask". X86 hardware -requires that these masks have all the '1' bits in a contiguous block. So -0x3, 0x6 and 0xC are legal 4-bit masks with two bits set, but 0x5, 0x9 -and 0xA are not. On a system with a 20-bit mask each bit represents 5% -of the capacity of the cache. You could partition the cache into four -equal parts with masks: 0x1f, 0x3e0, 0x7c00, 0xf8000. - -Memory bandwidth Allocation and monitoring ------------------------------------------- - -For Memory bandwidth resource, by default the user controls the resource -by indicating the percentage of total memory bandwidth. - -The minimum bandwidth percentage value for each cpu model is predefined -and can be looked up through "info/MB/min_bandwidth". The bandwidth -granularity that is allocated is also dependent on the cpu model and can -be looked up at "info/MB/bandwidth_gran". The available bandwidth -control steps are: min_bw + N * bw_gran. Intermediate values are rounded -to the next control step available on the hardware. - -The bandwidth throttling is a core specific mechanism on some of Intel -SKUs. Using a high bandwidth and a low bandwidth setting on two threads -sharing a core will result in both threads being throttled to use the -low bandwidth. The fact that Memory bandwidth allocation(MBA) is a core -specific mechanism where as memory bandwidth monitoring(MBM) is done at -the package level may lead to confusion when users try to apply control -via the MBA and then monitor the bandwidth to see if the controls are -effective. Below are such scenarios: - -1. User may *not* see increase in actual bandwidth when percentage - values are increased: - -This can occur when aggregate L2 external bandwidth is more than L3 -external bandwidth. Consider an SKL SKU with 24 cores on a package and -where L2 external is 10GBps (hence aggregate L2 external bandwidth is -240GBps) and L3 external bandwidth is 100GBps. Now a workload with '20 -threads, having 50% bandwidth, each consuming 5GBps' consumes the max L3 -bandwidth of 100GBps although the percentage value specified is only 50% -<< 100%. Hence increasing the bandwidth percentage will not yeild any -more bandwidth. This is because although the L2 external bandwidth still -has capacity, the L3 external bandwidth is fully used. Also note that -this would be dependent on number of cores the benchmark is run on. - -2. Same bandwidth percentage may mean different actual bandwidth - depending on # of threads: - -For the same SKU in #1, a 'single thread, with 10% bandwidth' and '4 -thread, with 10% bandwidth' can consume upto 10GBps and 40GBps although -they have same percentage bandwidth of 10%. This is simply because as -threads start using more cores in an rdtgroup, the actual bandwidth may -increase or vary although user specified bandwidth percentage is same. - -In order to mitigate this and make the interface more user friendly, -resctrl added support for specifying the bandwidth in MBps as well. The -kernel underneath would use a software feedback mechanism or a "Software -Controller(mba_sc)" which reads the actual bandwidth using MBM counters -and adjust the memowy bandwidth percentages to ensure - - "actual bandwidth < user specified bandwidth". - -By default, the schemata would take the bandwidth percentage values -where as user can switch to the "MBA software controller" mode using -a mount option 'mba_MBps'. The schemata format is specified in the below -sections. - -L3 schemata file details (code and data prioritization disabled) ----------------------------------------------------------------- -With CDP disabled the L3 schemata format is: - - L3:<cache_id0>=<cbm>;<cache_id1>=<cbm>;... - -L3 schemata file details (CDP enabled via mount option to resctrl) ------------------------------------------------------------------- -When CDP is enabled L3 control is split into two separate resources -so you can specify independent masks for code and data like this: - - L3data:<cache_id0>=<cbm>;<cache_id1>=<cbm>;... - L3code:<cache_id0>=<cbm>;<cache_id1>=<cbm>;... - -L2 schemata file details ------------------------- -L2 cache does not support code and data prioritization, so the -schemata format is always: - - L2:<cache_id0>=<cbm>;<cache_id1>=<cbm>;... - -Memory bandwidth Allocation (default mode) ------------------------------------------- - -Memory b/w domain is L3 cache. - - MB:<cache_id0>=bandwidth0;<cache_id1>=bandwidth1;... - -Memory bandwidth Allocation specified in MBps ---------------------------------------------- - -Memory bandwidth domain is L3 cache. - - MB:<cache_id0>=bw_MBps0;<cache_id1>=bw_MBps1;... - -Reading/writing the schemata file ---------------------------------- -Reading the schemata file will show the state of all resources -on all domains. When writing you only need to specify those values -which you wish to change. E.g. - -# cat schemata -L3DATA:0=fffff;1=fffff;2=fffff;3=fffff -L3CODE:0=fffff;1=fffff;2=fffff;3=fffff -# echo "L3DATA:2=3c0;" > schemata -# cat schemata -L3DATA:0=fffff;1=fffff;2=3c0;3=fffff -L3CODE:0=fffff;1=fffff;2=fffff;3=fffff - -Cache Pseudo-Locking --------------------- -CAT enables a user to specify the amount of cache space that an -application can fill. Cache pseudo-locking builds on the fact that a -CPU can still read and write data pre-allocated outside its current -allocated area on a cache hit. With cache pseudo-locking, data can be -preloaded into a reserved portion of cache that no application can -fill, and from that point on will only serve cache hits. The cache -pseudo-locked memory is made accessible to user space where an -application can map it into its virtual address space and thus have -a region of memory with reduced average read latency. - -The creation of a cache pseudo-locked region is triggered by a request -from the user to do so that is accompanied by a schemata of the region -to be pseudo-locked. The cache pseudo-locked region is created as follows: -- Create a CAT allocation CLOSNEW with a CBM matching the schemata - from the user of the cache region that will contain the pseudo-locked - memory. This region must not overlap with any current CAT allocation/CLOS - on the system and no future overlap with this cache region is allowed - while the pseudo-locked region exists. -- Create a contiguous region of memory of the same size as the cache - region. -- Flush the cache, disable hardware prefetchers, disable preemption. -- Make CLOSNEW the active CLOS and touch the allocated memory to load - it into the cache. -- Set the previous CLOS as active. -- At this point the closid CLOSNEW can be released - the cache - pseudo-locked region is protected as long as its CBM does not appear in - any CAT allocation. Even though the cache pseudo-locked region will from - this point on not appear in any CBM of any CLOS an application running with - any CLOS will be able to access the memory in the pseudo-locked region since - the region continues to serve cache hits. -- The contiguous region of memory loaded into the cache is exposed to - user-space as a character device. - -Cache pseudo-locking increases the probability that data will remain -in the cache via carefully configuring the CAT feature and controlling -application behavior. There is no guarantee that data is placed in -cache. Instructions like INVD, WBINVD, CLFLUSH, etc. can still evict -“locked” data from cache. Power management C-states may shrink or -power off cache. Deeper C-states will automatically be restricted on -pseudo-locked region creation. - -It is required that an application using a pseudo-locked region runs -with affinity to the cores (or a subset of the cores) associated -with the cache on which the pseudo-locked region resides. A sanity check -within the code will not allow an application to map pseudo-locked memory -unless it runs with affinity to cores associated with the cache on which the -pseudo-locked region resides. The sanity check is only done during the -initial mmap() handling, there is no enforcement afterwards and the -application self needs to ensure it remains affine to the correct cores. - -Pseudo-locking is accomplished in two stages: -1) During the first stage the system administrator allocates a portion - of cache that should be dedicated to pseudo-locking. At this time an - equivalent portion of memory is allocated, loaded into allocated - cache portion, and exposed as a character device. -2) During the second stage a user-space application maps (mmap()) the - pseudo-locked memory into its address space. - -Cache Pseudo-Locking Interface ------------------------------- -A pseudo-locked region is created using the resctrl interface as follows: - -1) Create a new resource group by creating a new directory in /sys/fs/resctrl. -2) Change the new resource group's mode to "pseudo-locksetup" by writing - "pseudo-locksetup" to the "mode" file. -3) Write the schemata of the pseudo-locked region to the "schemata" file. All - bits within the schemata should be "unused" according to the "bit_usage" - file. - -On successful pseudo-locked region creation the "mode" file will contain -"pseudo-locked" and a new character device with the same name as the resource -group will exist in /dev/pseudo_lock. This character device can be mmap()'ed -by user space in order to obtain access to the pseudo-locked memory region. - -An example of cache pseudo-locked region creation and usage can be found below. - -Cache Pseudo-Locking Debugging Interface ---------------------------------------- -The pseudo-locking debugging interface is enabled by default (if -CONFIG_DEBUG_FS is enabled) and can be found in /sys/kernel/debug/resctrl. - -There is no explicit way for the kernel to test if a provided memory -location is present in the cache. The pseudo-locking debugging interface uses -the tracing infrastructure to provide two ways to measure cache residency of -the pseudo-locked region: -1) Memory access latency using the pseudo_lock_mem_latency tracepoint. Data - from these measurements are best visualized using a hist trigger (see - example below). In this test the pseudo-locked region is traversed at - a stride of 32 bytes while hardware prefetchers and preemption - are disabled. This also provides a substitute visualization of cache - hits and misses. -2) Cache hit and miss measurements using model specific precision counters if - available. Depending on the levels of cache on the system the pseudo_lock_l2 - and pseudo_lock_l3 tracepoints are available. - -When a pseudo-locked region is created a new debugfs directory is created for -it in debugfs as /sys/kernel/debug/resctrl/<newdir>. A single -write-only file, pseudo_lock_measure, is present in this directory. The -measurement of the pseudo-locked region depends on the number written to this -debugfs file: -1 - writing "1" to the pseudo_lock_measure file will trigger the latency - measurement captured in the pseudo_lock_mem_latency tracepoint. See - example below. -2 - writing "2" to the pseudo_lock_measure file will trigger the L2 cache - residency (cache hits and misses) measurement captured in the - pseudo_lock_l2 tracepoint. See example below. -3 - writing "3" to the pseudo_lock_measure file will trigger the L3 cache - residency (cache hits and misses) measurement captured in the - pseudo_lock_l3 tracepoint. - -All measurements are recorded with the tracing infrastructure. This requires -the relevant tracepoints to be enabled before the measurement is triggered. - -Example of latency debugging interface: -In this example a pseudo-locked region named "newlock" was created. Here is -how we can measure the latency in cycles of reading from this region and -visualize this data with a histogram that is available if CONFIG_HIST_TRIGGERS -is set: -# :> /sys/kernel/debug/tracing/trace -# echo 'hist:keys=latency' > /sys/kernel/debug/tracing/events/resctrl/pseudo_lock_mem_latency/trigger -# echo 1 > /sys/kernel/debug/tracing/events/resctrl/pseudo_lock_mem_latency/enable -# echo 1 > /sys/kernel/debug/resctrl/newlock/pseudo_lock_measure -# echo 0 > /sys/kernel/debug/tracing/events/resctrl/pseudo_lock_mem_latency/enable -# cat /sys/kernel/debug/tracing/events/resctrl/pseudo_lock_mem_latency/hist - -# event histogram -# -# trigger info: hist:keys=latency:vals=hitcount:sort=hitcount:size=2048 [active] -# - -{ latency: 456 } hitcount: 1 -{ latency: 50 } hitcount: 83 -{ latency: 36 } hitcount: 96 -{ latency: 44 } hitcount: 174 -{ latency: 48 } hitcount: 195 -{ latency: 46 } hitcount: 262 -{ latency: 42 } hitcount: 693 -{ latency: 40 } hitcount: 3204 -{ latency: 38 } hitcount: 3484 - -Totals: - Hits: 8192 - Entries: 9 - Dropped: 0 - -Example of cache hits/misses debugging: -In this example a pseudo-locked region named "newlock" was created on the L2 -cache of a platform. Here is how we can obtain details of the cache hits -and misses using the platform's precision counters. - -# :> /sys/kernel/debug/tracing/trace -# echo 1 > /sys/kernel/debug/tracing/events/resctrl/pseudo_lock_l2/enable -# echo 2 > /sys/kernel/debug/resctrl/newlock/pseudo_lock_measure -# echo 0 > /sys/kernel/debug/tracing/events/resctrl/pseudo_lock_l2/enable -# cat /sys/kernel/debug/tracing/trace - -# tracer: nop -# -# _-----=> irqs-off -# / _----=> need-resched -# | / _---=> hardirq/softirq -# || / _--=> preempt-depth -# ||| / delay -# TASK-PID CPU# |||| TIMESTAMP FUNCTION -# | | | |||| | | - pseudo_lock_mea-1672 [002] .... 3132.860500: pseudo_lock_l2: hits=4097 miss=0 - - -Examples for RDT allocation usage: - -Example 1 ---------- -On a two socket machine (one L3 cache per socket) with just four bits -for cache bit masks, minimum b/w of 10% with a memory bandwidth -granularity of 10% - -# mount -t resctrl resctrl /sys/fs/resctrl -# cd /sys/fs/resctrl -# mkdir p0 p1 -# echo "L3:0=3;1=c\nMB:0=50;1=50" > /sys/fs/resctrl/p0/schemata -# echo "L3:0=3;1=3\nMB:0=50;1=50" > /sys/fs/resctrl/p1/schemata - -The default resource group is unmodified, so we have access to all parts -of all caches (its schemata file reads "L3:0=f;1=f"). - -Tasks that are under the control of group "p0" may only allocate from the -"lower" 50% on cache ID 0, and the "upper" 50% of cache ID 1. -Tasks in group "p1" use the "lower" 50% of cache on both sockets. - -Similarly, tasks that are under the control of group "p0" may use a -maximum memory b/w of 50% on socket0 and 50% on socket 1. -Tasks in group "p1" may also use 50% memory b/w on both sockets. -Note that unlike cache masks, memory b/w cannot specify whether these -allocations can overlap or not. The allocations specifies the maximum -b/w that the group may be able to use and the system admin can configure -the b/w accordingly. - -If the MBA is specified in MB(megabytes) then user can enter the max b/w in MB -rather than the percentage values. - -# echo "L3:0=3;1=c\nMB:0=1024;1=500" > /sys/fs/resctrl/p0/schemata -# echo "L3:0=3;1=3\nMB:0=1024;1=500" > /sys/fs/resctrl/p1/schemata - -In the above example the tasks in "p1" and "p0" on socket 0 would use a max b/w -of 1024MB where as on socket 1 they would use 500MB. - -Example 2 ---------- -Again two sockets, but this time with a more realistic 20-bit mask. - -Two real time tasks pid=1234 running on processor 0 and pid=5678 running on -processor 1 on socket 0 on a 2-socket and dual core machine. To avoid noisy -neighbors, each of the two real-time tasks exclusively occupies one quarter -of L3 cache on socket 0. - -# mount -t resctrl resctrl /sys/fs/resctrl -# cd /sys/fs/resctrl - -First we reset the schemata for the default group so that the "upper" -50% of the L3 cache on socket 0 and 50% of memory b/w cannot be used by -ordinary tasks: - -# echo "L3:0=3ff;1=fffff\nMB:0=50;1=100" > schemata - -Next we make a resource group for our first real time task and give -it access to the "top" 25% of the cache on socket 0. - -# mkdir p0 -# echo "L3:0=f8000;1=fffff" > p0/schemata - -Finally we move our first real time task into this resource group. We -also use taskset(1) to ensure the task always runs on a dedicated CPU -on socket 0. Most uses of resource groups will also constrain which -processors tasks run on. - -# echo 1234 > p0/tasks -# taskset -cp 1 1234 - -Ditto for the second real time task (with the remaining 25% of cache): - -# mkdir p1 -# echo "L3:0=7c00;1=fffff" > p1/schemata -# echo 5678 > p1/tasks -# taskset -cp 2 5678 - -For the same 2 socket system with memory b/w resource and CAT L3 the -schemata would look like(Assume min_bandwidth 10 and bandwidth_gran is -10): - -For our first real time task this would request 20% memory b/w on socket -0. - -# echo -e "L3:0=f8000;1=fffff\nMB:0=20;1=100" > p0/schemata - -For our second real time task this would request an other 20% memory b/w -on socket 0. - -# echo -e "L3:0=f8000;1=fffff\nMB:0=20;1=100" > p0/schemata - -Example 3 ---------- - -A single socket system which has real-time tasks running on core 4-7 and -non real-time workload assigned to core 0-3. The real-time tasks share text -and data, so a per task association is not required and due to interaction -with the kernel it's desired that the kernel on these cores shares L3 with -the tasks. - -# mount -t resctrl resctrl /sys/fs/resctrl -# cd /sys/fs/resctrl - -First we reset the schemata for the default group so that the "upper" -50% of the L3 cache on socket 0, and 50% of memory bandwidth on socket 0 -cannot be used by ordinary tasks: - -# echo "L3:0=3ff\nMB:0=50" > schemata - -Next we make a resource group for our real time cores and give it access -to the "top" 50% of the cache on socket 0 and 50% of memory bandwidth on -socket 0. - -# mkdir p0 -# echo "L3:0=ffc00\nMB:0=50" > p0/schemata - -Finally we move core 4-7 over to the new group and make sure that the -kernel and the tasks running there get 50% of the cache. They should -also get 50% of memory bandwidth assuming that the cores 4-7 are SMT -siblings and only the real time threads are scheduled on the cores 4-7. - -# echo F0 > p0/cpus - -Example 4 ---------- - -The resource groups in previous examples were all in the default "shareable" -mode allowing sharing of their cache allocations. If one resource group -configures a cache allocation then nothing prevents another resource group -to overlap with that allocation. - -In this example a new exclusive resource group will be created on a L2 CAT -system with two L2 cache instances that can be configured with an 8-bit -capacity bitmask. The new exclusive resource group will be configured to use -25% of each cache instance. - -# mount -t resctrl resctrl /sys/fs/resctrl/ -# cd /sys/fs/resctrl - -First, we observe that the default group is configured to allocate to all L2 -cache: - -# cat schemata -L2:0=ff;1=ff - -We could attempt to create the new resource group at this point, but it will -fail because of the overlap with the schemata of the default group: -# mkdir p0 -# echo 'L2:0=0x3;1=0x3' > p0/schemata -# cat p0/mode -shareable -# echo exclusive > p0/mode --sh: echo: write error: Invalid argument -# cat info/last_cmd_status -schemata overlaps - -To ensure that there is no overlap with another resource group the default -resource group's schemata has to change, making it possible for the new -resource group to become exclusive. -# echo 'L2:0=0xfc;1=0xfc' > schemata -# echo exclusive > p0/mode -# grep . p0/* -p0/cpus:0 -p0/mode:exclusive -p0/schemata:L2:0=03;1=03 -p0/size:L2:0=262144;1=262144 - -A new resource group will on creation not overlap with an exclusive resource -group: -# mkdir p1 -# grep . p1/* -p1/cpus:0 -p1/mode:shareable -p1/schemata:L2:0=fc;1=fc -p1/size:L2:0=786432;1=786432 - -The bit_usage will reflect how the cache is used: -# cat info/L2/bit_usage -0=SSSSSSEE;1=SSSSSSEE - -A resource group cannot be forced to overlap with an exclusive resource group: -# echo 'L2:0=0x1;1=0x1' > p1/schemata --sh: echo: write error: Invalid argument -# cat info/last_cmd_status -overlaps with exclusive group - -Example of Cache Pseudo-Locking -------------------------------- -Lock portion of L2 cache from cache id 1 using CBM 0x3. Pseudo-locked -region is exposed at /dev/pseudo_lock/newlock that can be provided to -application for argument to mmap(). - -# mount -t resctrl resctrl /sys/fs/resctrl/ -# cd /sys/fs/resctrl - -Ensure that there are bits available that can be pseudo-locked, since only -unused bits can be pseudo-locked the bits to be pseudo-locked needs to be -removed from the default resource group's schemata: -# cat info/L2/bit_usage -0=SSSSSSSS;1=SSSSSSSS -# echo 'L2:1=0xfc' > schemata -# cat info/L2/bit_usage -0=SSSSSSSS;1=SSSSSS00 - -Create a new resource group that will be associated with the pseudo-locked -region, indicate that it will be used for a pseudo-locked region, and -configure the requested pseudo-locked region capacity bitmask: - -# mkdir newlock -# echo pseudo-locksetup > newlock/mode -# echo 'L2:1=0x3' > newlock/schemata - -On success the resource group's mode will change to pseudo-locked, the -bit_usage will reflect the pseudo-locked region, and the character device -exposing the pseudo-locked region will exist: - -# cat newlock/mode -pseudo-locked -# cat info/L2/bit_usage -0=SSSSSSSS;1=SSSSSSPP -# ls -l /dev/pseudo_lock/newlock -crw------- 1 root root 243, 0 Apr 3 05:01 /dev/pseudo_lock/newlock - -/* - * Example code to access one page of pseudo-locked cache region - * from user space. - */ -#define _GNU_SOURCE -#include <fcntl.h> -#include <sched.h> -#include <stdio.h> -#include <stdlib.h> -#include <unistd.h> -#include <sys/mman.h> - -/* - * It is required that the application runs with affinity to only - * cores associated with the pseudo-locked region. Here the cpu - * is hardcoded for convenience of example. - */ -static int cpuid = 2; - -int main(int argc, char *argv[]) -{ - cpu_set_t cpuset; - long page_size; - void *mapping; - int dev_fd; - int ret; - - page_size = sysconf(_SC_PAGESIZE); - - CPU_ZERO(&cpuset); - CPU_SET(cpuid, &cpuset); - ret = sched_setaffinity(0, sizeof(cpuset), &cpuset); - if (ret < 0) { - perror("sched_setaffinity"); - exit(EXIT_FAILURE); - } - - dev_fd = open("/dev/pseudo_lock/newlock", O_RDWR); - if (dev_fd < 0) { - perror("open"); - exit(EXIT_FAILURE); - } - - mapping = mmap(0, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, - dev_fd, 0); - if (mapping == MAP_FAILED) { - perror("mmap"); - close(dev_fd); - exit(EXIT_FAILURE); - } - - /* Application interacts with pseudo-locked memory @mapping */ - - ret = munmap(mapping, page_size); - if (ret < 0) { - perror("munmap"); - close(dev_fd); - exit(EXIT_FAILURE); - } - - close(dev_fd); - exit(EXIT_SUCCESS); -} - -Locking between applications ----------------------------- - -Certain operations on the resctrl filesystem, composed of read/writes -to/from multiple files, must be atomic. - -As an example, the allocation of an exclusive reservation of L3 cache -involves: - - 1. Read the cbmmasks from each directory or the per-resource "bit_usage" - 2. Find a contiguous set of bits in the global CBM bitmask that is clear - in any of the directory cbmmasks - 3. Create a new directory - 4. Set the bits found in step 2 to the new directory "schemata" file - -If two applications attempt to allocate space concurrently then they can -end up allocating the same bits so the reservations are shared instead of -exclusive. - -To coordinate atomic operations on the resctrlfs and to avoid the problem -above, the following locking procedure is recommended: - -Locking is based on flock, which is available in libc and also as a shell -script command - -Write lock: - - A) Take flock(LOCK_EX) on /sys/fs/resctrl - B) Read/write the directory structure. - C) funlock - -Read lock: - - A) Take flock(LOCK_SH) on /sys/fs/resctrl - B) If success read the directory structure. - C) funlock - -Example with bash: - -# Atomically read directory structure -$ flock -s /sys/fs/resctrl/ find /sys/fs/resctrl - -# Read directory contents and create new subdirectory - -$ cat create-dir.sh -find /sys/fs/resctrl/ > output.txt -mask = function-of(output.txt) -mkdir /sys/fs/resctrl/newres/ -echo mask > /sys/fs/resctrl/newres/schemata - -$ flock /sys/fs/resctrl/ ./create-dir.sh - -Example with C: - -/* - * Example code do take advisory locks - * before accessing resctrl filesystem - */ -#include <sys/file.h> -#include <stdlib.h> - -void resctrl_take_shared_lock(int fd) -{ - int ret; - - /* take shared lock on resctrl filesystem */ - ret = flock(fd, LOCK_SH); - if (ret) { - perror("flock"); - exit(-1); - } -} - -void resctrl_take_exclusive_lock(int fd) -{ - int ret; - - /* release lock on resctrl filesystem */ - ret = flock(fd, LOCK_EX); - if (ret) { - perror("flock"); - exit(-1); - } -} - -void resctrl_release_lock(int fd) -{ - int ret; - - /* take shared lock on resctrl filesystem */ - ret = flock(fd, LOCK_UN); - if (ret) { - perror("flock"); - exit(-1); - } -} - -void main(void) -{ - int fd, ret; - - fd = open("/sys/fs/resctrl", O_DIRECTORY); - if (fd == -1) { - perror("open"); - exit(-1); - } - resctrl_take_shared_lock(fd); - /* code to read directory contents */ - resctrl_release_lock(fd); - - resctrl_take_exclusive_lock(fd); - /* code to read and write directory contents */ - resctrl_release_lock(fd); -} - -Examples for RDT Monitoring along with allocation usage: - -Reading monitored data ----------------------- -Reading an event file (for ex: mon_data/mon_L3_00/llc_occupancy) would -show the current snapshot of LLC occupancy of the corresponding MON -group or CTRL_MON group. - - -Example 1 (Monitor CTRL_MON group and subset of tasks in CTRL_MON group) ---------- -On a two socket machine (one L3 cache per socket) with just four bits -for cache bit masks - -# mount -t resctrl resctrl /sys/fs/resctrl -# cd /sys/fs/resctrl -# mkdir p0 p1 -# echo "L3:0=3;1=c" > /sys/fs/resctrl/p0/schemata -# echo "L3:0=3;1=3" > /sys/fs/resctrl/p1/schemata -# echo 5678 > p1/tasks -# echo 5679 > p1/tasks - -The default resource group is unmodified, so we have access to all parts -of all caches (its schemata file reads "L3:0=f;1=f"). - -Tasks that are under the control of group "p0" may only allocate from the -"lower" 50% on cache ID 0, and the "upper" 50% of cache ID 1. -Tasks in group "p1" use the "lower" 50% of cache on both sockets. - -Create monitor groups and assign a subset of tasks to each monitor group. - -# cd /sys/fs/resctrl/p1/mon_groups -# mkdir m11 m12 -# echo 5678 > m11/tasks -# echo 5679 > m12/tasks - -fetch data (data shown in bytes) - -# cat m11/mon_data/mon_L3_00/llc_occupancy -16234000 -# cat m11/mon_data/mon_L3_01/llc_occupancy -14789000 -# cat m12/mon_data/mon_L3_00/llc_occupancy -16789000 - -The parent ctrl_mon group shows the aggregated data. - -# cat /sys/fs/resctrl/p1/mon_data/mon_l3_00/llc_occupancy -31234000 - -Example 2 (Monitor a task from its creation) ---------- -On a two socket machine (one L3 cache per socket) - -# mount -t resctrl resctrl /sys/fs/resctrl -# cd /sys/fs/resctrl -# mkdir p0 p1 - -An RMID is allocated to the group once its created and hence the <cmd> -below is monitored from its creation. - -# echo $$ > /sys/fs/resctrl/p1/tasks -# <cmd> - -Fetch the data - -# cat /sys/fs/resctrl/p1/mon_data/mon_l3_00/llc_occupancy -31789000 - -Example 3 (Monitor without CAT support or before creating CAT groups) ---------- - -Assume a system like HSW has only CQM and no CAT support. In this case -the resctrl will still mount but cannot create CTRL_MON directories. -But user can create different MON groups within the root group thereby -able to monitor all tasks including kernel threads. - -This can also be used to profile jobs cache size footprint before being -able to allocate them to different allocation groups. - -# mount -t resctrl resctrl /sys/fs/resctrl -# cd /sys/fs/resctrl -# mkdir mon_groups/m01 -# mkdir mon_groups/m02 - -# echo 3478 > /sys/fs/resctrl/mon_groups/m01/tasks -# echo 2467 > /sys/fs/resctrl/mon_groups/m02/tasks - -Monitor the groups separately and also get per domain data. From the -below its apparent that the tasks are mostly doing work on -domain(socket) 0. - -# cat /sys/fs/resctrl/mon_groups/m01/mon_L3_00/llc_occupancy -31234000 -# cat /sys/fs/resctrl/mon_groups/m01/mon_L3_01/llc_occupancy -34555 -# cat /sys/fs/resctrl/mon_groups/m02/mon_L3_00/llc_occupancy -31234000 -# cat /sys/fs/resctrl/mon_groups/m02/mon_L3_01/llc_occupancy -32789 - - -Example 4 (Monitor real time tasks) ------------------------------------ - -A single socket system which has real time tasks running on cores 4-7 -and non real time tasks on other cpus. We want to monitor the cache -occupancy of the real time threads on these cores. - -# mount -t resctrl resctrl /sys/fs/resctrl -# cd /sys/fs/resctrl -# mkdir p1 - -Move the cpus 4-7 over to p1 -# echo f0 > p1/cpus - -View the llc occupancy snapshot - -# cat /sys/fs/resctrl/p1/mon_data/mon_L3_00/llc_occupancy -11234000 |