kernel/linux.git/tools/testing/selftests/resctrl/resctrl_val.c, branch v6.19.11

selftests/resctrl: Ensure measurements skip initialization of default benchmark

2024-11-05T00:02:03+00:00

The CMT, MBA, and MBM tests rely on the resctrl_val() wrapper to start and run a benchmark while providing test specific flows via callbacks to do test specific configuration and measurements. At a high level, the resctrl_val() flow is: a) Start by fork()ing a child process that installs a signal handler for SIGUSR1 that, on receipt of SIGUSR1, will start running a benchmark. b) Assign the child process created in (a) to the resctrl control and monitoring group that dictates the memory and cache allocations with which the process can run and will contain all resctrl monitoring data of that process. c) Once parent and child are considered "ready" (determined via a message over a pipe) the parent signals the child (via SIGUSR1) to start the benchmark, waits one second for the benchmark to run, and then starts collecting monitoring data for the tests, potentially also changing allocation configuration depending on the various test callbacks. A problem with the above flow is the "black box" view of the benchmark that is combined with an arbitrarily chosen "wait one second" before measurements start. No matter what the benchmark does, it is given one second to initialize before measurements start. The default benchmark "fill_buf" consists of two parts, first it prepares a buffer (allocate, initialize, then flush), then it reads from the buffer (in unpredictable ways) until terminated. Depending on the system and the size of the buffer, the first "prepare" part may not be complete by the time the one second delay expires. Test measurements may thus start before the work needing to be measured runs. Split the default benchmark into its "prepare" and "runtime" parts and simplify the resctrl_val() wrapper while doing so. This same split cannot be done for the user provided benchmark (without a user interface change), so the current behavior is maintained for user provided benchmark. Assign the test itself to the control and monitoring group and run the "prepare" part of the benchmark in this context, ensuring it runs with required cache and memory bandwidth allocations. With the benchmark preparation complete it is only needed to fork() the "runtime" part of the benchmark (or entire user provided benchmark). Keep the "wait one second" delay before measurements start. For the default "fill_buf" benchmark this time now covers only the "runtime" portion that needs to be measured. For the user provided benchmark this delay maintains current behavior. Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen Signed-off-by: Shuah Khan

selftests/resctrl: Make benchmark parameter passing robust

2024-11-05T00:02:03+00:00

The benchmark used during the CMT, MBM, and MBA tests can be provided by the user via (-b) parameter, if not provided the default "fill_buf" benchmark is used. The user is additionally able to override any of the "fill_buf" default parameters when running the tests with "-b fill_buf ". The "fill_buf" parameters are managed as an array of strings. Using an array of strings is complex because it requires transformations to/from strings at every producer and consumer. This is made worse for the individual tests where the default benchmark parameters values may not be appropriate and additional data wrangling is required. For example, the CMT test duplicates the entire array of strings in order to replace one of the parameters. More issues appear when combining the usage of an array of strings with the use case of user overriding default parameters by specifying "-b fill_buf ". This use case is fragile with opportunities to trigger a SIGSEGV because of opportunities for NULL pointers to exist in the array of strings. For example, by running below (thus by specifying "fill_buf" should be used but all parameters are NULL): $ sudo resctrl_tests -t mbm -b fill_buf Replace the "array of strings" parameters used for "fill_buf" with new struct fill_buf_param that contains the "fill_buf" parameters that can be used directly without transformations to/from strings. Two instances of struct fill_buf_param may exist at any point in time: * If the user provides new parameters to "fill_buf", the user parameter structure (struct user_params) will point to a fully initialized and immutable struct fill_buf_param containing the user provided parameters. * If "fill_buf" is the benchmark that should be used by a test, then the test parameter structure (struct resctrl_val_param) will point to a fully initialized struct fill_buf_param. The latter may contain (a) the user provided parameters verbatim, (b) user provided parameters adjusted to be appropriate for the test, or (c) the default parameters for "fill_buf" that is appropriate for the test if the user did not provide "fill_buf" parameters nor an alternate benchmark. The existing behavior of CMT test is to use test defined value for the buffer size even if the user provides another value via command line. This behavior is maintained since the test requires that the buffer size matches the size of the cache allocated, and the amount of cache allocated can instead be changed by the user with the "-n" command line parameter. Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen Signed-off-by: Shuah Khan

selftests/resctrl: Remove unused measurement code

2024-11-05T00:02:03+00:00

The MBM and MBA resctrl selftests run a benchmark during which it takes measurements of read memory bandwidth via perf. Code exists to support measurements of write memory bandwidth but there exists no path with which this code can execute. While code exists for write memory bandwidth measurement there has not yet been a use case for it. Remove this unused code. Rename relevant functions to include "read" so that it is clear that it relates only to memory bandwidth reads, while renaming the functions also add consistency by changing the "membw" instances to more prevalent "mem_bw". Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen Signed-off-by: Shuah Khan

selftests/resctrl: Only support measured read operation

2024-11-05T00:02:03+00:00

The CMT, MBM, and MBA tests rely on a benchmark to generate memory traffic. By default this is the "fill_buf" benchmark that can be replaced via the "-b" command line argument. The original intent of the "-b" command line parameter was to replace the default "fill_buf" benchmark, but the implementation also exposes an alternative use case where the "fill_buf" parameters itself can be modified. One of the parameters to "fill_buf" is the "operation" that can be either "read" or "write" and indicates whether the "fill_buf" should use "read" or "write" operations on the allocated buffer. While replacing "fill_buf" default parameters is technically possible, replacing the default "read" parameter with "write" is not supported because the MBA and MBM tests only measure "read" operations. The "read" operation is also most appropriate for the CMT test that aims to use the benchmark to allocate into the cache. Avoid any potential inconsistencies between test and measurement by removing code for unsupported "write" operations to the buffer. Ignore any attempt from user space to enable this unsupported test configuration, instead always use read operations. Keep the initialization of the, now unused, "fill_buf" parameters to reserve these parameter positions since it has been exposed as an API. Future parameter additions cannot use these parameter positions. Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen Signed-off-by: Shuah Khan

selftests/resctrl: Remove "once" parameter required to be false

2024-11-05T00:02:03+00:00

The CMT, MBM, and MBA tests rely on a benchmark that runs while the test makes changes to needed configuration (for example memory bandwidth allocation) and takes needed measurements. By default the "fill_buf" benchmark is used and by default (via its "once = false" setting) "fill_buf" is configured to run until terminated after the test completes. An unintended consequence of enabling the user to override the benchmark also enables the user to change parameters to the "fill_buf" benchmark. This enables the user to set "fill_buf" to only cycle through the buffer once (by setting "once = true") and thus breaking the CMT, MBA, and MBM tests that expect workload/interference to be reflected by their measurements. Prevent user space from changing the "once" parameter and ensure that it is always false for the CMT, MBA, and MBM tests. Suggested-by: Ilpo Järvinen Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen Signed-off-by: Shuah Khan

selftests/resctrl: Protect against array overflow when reading strings

2024-11-05T00:02:02+00:00

resctrl selftests discover system properties via a variety of sysfs files. The MBM and MBA tests need to discover the event and umask with which to configure the performance event used to measure read memory bandwidth. This is done by parsing the contents of /sys/bus/event_source/devices/uncore_imc_/events/cas_count_read Similarly, the resctrl selftests discover the cache size via /sys/bus/cpu/devices/cpu/cache/index/size. Take care to do bounds checking when using fscanf() to read the contents of files into a string buffer because by default fscanf() assumes arbitrarily long strings. If the file contains more bytes than the array can accommodate then an overflow will occur. Provide a maximum field width to the conversion specifier to protect against array overflow. The maximum is one less than the array size because string input stores a terminating null byte that is not covered by the maximum field width. Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen Signed-off-by: Shuah Khan

selftests/resctrl: Protect against array overrun during iMC config parsing

2024-11-05T00:02:02+00:00

The MBM and MBA tests need to discover the event and umask with which to configure the performance event used to measure read memory bandwidth. This is done by parsing the /sys/bus/event_source/devices/uncore_imc_/events/cas_count_read file for each iMC instance that contains the formatted output: "event=,umask=" Parsing of cas_count_read contents is done by initializing an array of MAX_TOKENS elements with tokens (deliminated by "=,") from this file. Remove the unnecessary append of a delimiter to the string needing to be parsed. Per the strtok() man page: "delimiter bytes at the start or end of the string are ignored". This has no impact on the token placement within the array. After initialization, the actual event and umask is determined by parsing the tokens directly following the "event" and "umask" tokens respectively. Iterating through the array up to index "i < MAX_TOKENS" but then accessing index "i + 1" risks array overrun during the final iteration. Avoid array overrun by ensuring that the index used within for loop will always be valid. Fixes: 1d3f08687d76 ("selftests/resctrl: Read memory bandwidth from perf IMC counter and from resctrl file system") Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen Signed-off-by: Shuah Khan

selftests/resctrl: Make functions only used in same file static

2024-11-05T00:02:02+00:00

Fix following sparse warnings: tools/testing/selftests/resctrl/resctrl_val.c:47:6: warning: symbol 'membw_initialize_perf_event_attr' was not declared. Should it be static? tools/testing/selftests/resctrl/resctrl_val.c:64:6: warning: symbol 'membw_ioctl_perf_event_ioc_reset_enable' was not declared. Should it be static? tools/testing/selftests/resctrl/resctrl_val.c:70:6: warning: symbol 'membw_ioctl_perf_event_ioc_disable' was not declared. Should it be static? tools/testing/selftests/resctrl/resctrl_val.c:81:6: warning: symbol 'get_event_and_umask' was not declared. Should it be static? Signed-off-by: Reinette Chatre Reviewed-by: Ilpo Järvinen Signed-off-by: Shuah Khan

selftests/resctrl: Remove test name comparing from write_bm_pid_to_resctrl()

2024-07-11T17:23:54+00:00

write_bm_pid_to_resctrl() uses resctrl_val to check test name which is not a good interface generic resctrl FS functions should provide. Tests define mongrp when needed. Remove the test name check in write_bm_pid_to_resctrl() to only rely on the mongrp parameter being non-NULL. Remove write_bm_pid_to_resctrl() resctrl_val parameter and resctrl_val member from the struct resctrl_val_param that are not used anymore. Similarly, remove the test name constants that are no longer used. Signed-off-by: Ilpo Järvinen Tested-by: Babu Moger Reviewed-by: Reinette Chatre Signed-off-by: Shuah Khan

selftests/resctrl: Simplify bandwidth report type handling

2024-07-11T17:23:54+00:00

bw_report is only needed for selecting the correct value from the values IMC measured. It is a member in the resctrl_val_param struct and is always set to "reads". The value is then checked in resctrl_val() using validate_bw_report_request() that besides validating the input, assumes it can mutate the string which is questionable programming practice. Simplify handling bw_report: - Convert validate_bw_report_request() into get_bw_report_type() that inputs and returns const char *. Use NULL to indicate error. - Validate the report types inside measure_mem_bw(), not in resctrl_val(). - Pass bw_report to measure_mem_bw() from ->measure() hook because resctrl_val() no longer needs bw_report for anything. Signed-off-by: Ilpo Järvinen Tested-by: Babu Moger Reviewed-by: Reinette Chatre Signed-off-by: Shuah Khan