BMC/Intel-BMC/linux.git/arch/s390/kernel/vtime.c, branch dev-4.6

s390/vtime: correct scaled cputime of partially idle CPUs

2015-09-30T14:22:38+00:00

The calculation for the SMT scaling factor for a hardware thread which has been partially idle needs to disregard the cycles spent by the other threads of the core while the thread is idle. Signed-off-by: Martin Schwidefsky

s390/vtime: correct scaled cputime for SMT

2015-09-17T11:43:43+00:00

The scaled cputime is supposed to be derived from the normal per-thread cputime by dividing it with the average thread density in the last interval. The calculation of the scaling values for the average thread density is incorrect. The current, incorrect calculation: Ci = cycle count with i active threads T = unscaled cputime, sT = scaled cputime sT = T * (C1 + C2 + ... + Cn) / (1*C1 + 2*C2 + ... + n*Cn) The calculation happens to yield the correct numbers for the simple cases with only one Ci value not zero. But for cases with multiple Ci values not zero it fails. E.g. on a SMT-2 system with one thread active half the time and two threads active for the other half of the time it fails, the scaling factor should be 3/4 but the formula gives 2/3. The correct formula is sT = T * (C1/1 + C2/2 + ... + Cn/n) / (C1 + C2 + ... + Cn) Signed-off-by: Martin Schwidefsky

s390/vtime: limit MT scaling value updates

2015-08-04T12:26:17+00:00

The MT scaling values are updated on each calll to do_account_vtime. This function is called for each HZ interrupt and for each context switch. Context switch can happen often, the STCCTM instruction on this path is noticeable. Limit the updates to once per jiffy. Signed-off-by: Martin Schwidefsky

s390: add SMT support

2015-01-22T11:16:01+00:00

The multi-threading facility is introduced with the z13 processor family. This patch adds code to detect the multi-threading facility. With the facility enabled each core will surface multiple hardware threads to the system. Each hardware threads looks like a normal CPU to the operating system with all its registers and properties. The SCLP interface reports the SMT topology indirectly via the maximum thread id. Each reported CPU in the result of a read-scp-information is a core representing a number of hardware threads. To reflect the reduced CPU capacity if two hardware threads run on a single core the MT utilization counter set is used to normalize the raw cputime obtained by the CPU timer deltas. This scaled cputime is reported via the taskstats interface. The normal /proc/stat numbers are based on the raw cputime and are not affected by the normalization. Signed-off-by: Martin Schwidefsky

s390/vtime: Get rid of redundant WARN_ON

2014-12-18T08:55:56+00:00

in the cpu time accounting function vtime_account_irq_enter (vtime_account_system) we use a WARN_ON_ONCE(!irqs_disabled()). This is redundant as the function virt_timer_forward is always called and has a BUG_ON(!irqs_disabled()). This saves several nanoseconds in my specific testcase (KVM entry/exit) and probably all other callers like (soft)irq entry/exit. Signed-off-by: Christian Borntraeger Reviewed-by: Heiko Carstens Signed-off-by: Martin Schwidefsky

s390/time: use stck clock fast for do_account_vtime

2014-10-27T12:27:01+00:00

The last high frequency call site of the STCK instruction is do_account_vtime. Replace it with the faster STCKF instruction. Signed-off-by: Martin Schwidefsky

s390/idle: consolidate idle functions and definitions

2014-10-09T07:14:03+00:00

Move the C functions and definitions related to the idle state handling to arch/s390/include/asm/idle.h and arch/s390/kernel/idle.c. The function s390_get_idle_time is renamed to arch_cpu_idle_time and vtime_stop_cpu to enabled_wait. Signed-off-by: Martin Schwidefsky

s390/nohz: use a per-cpu flag for arch_needs_cpu

2014-10-09T07:14:02+00:00

Move the nohz_delay bit from the s390_idle data structure to the per-cpu flags. Clear the nohz delay flag in __cpu_disable and remove the cpu hotplug notifier that used to do this. Signed-off-by: Martin Schwidefsky

s390/vtime: correct idle time calculation

2013-10-31T08:52:52+00:00

Use the ACCESS_ONCE macro for both accesses to idle->sequence in the loops to calculate the idle time. If only one access uses the macro, the compiler is free to cache the value for the second access which can cause endless loops. Cc: stable@vger.kernel.org # 3.6+ Signed-off-by: Martin Schwidefsky

s390/uaccess: always run the kernel in home space

2013-10-24T15:16:57+00:00

Simplify the uaccess code by removing the user_mode=home option. The kernel will now always run in the home space mode. Signed-off-by: Martin Schwidefsky