From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com> Hi,
This is the third version of the patches to track and expose idle PURR and SPURR ticks. These patches are required by tools such as lparstat to compute system utilization for capacity planning purposes. The previous versions can be found here: v2: https://lkml.org/lkml/2020/2/21/21 v1: https://lore.kernel.org/patchwork/cover/1159341/ They key changes from v2 are: - The prolog and epilog functions have been named pseries_idle_prolog() and pseries_idle_epilog() respectively to indicate their pseries specific nature. - Fixed the Documentation for /sys/devices/system/cpu/cpuX/idle_spurr as pointed out by Nathan Lynch. - Introduces a patch (Patch 6/6) to send an IPI in order to read and cache the values of purr, spurr, idle_purr and idle_spurr of the target CPU when any one of them is read via sysfs. These cached values will be presented if any of these sysfs are read within the next 10ms. If these sysfs files are read after 10ms from the earlier IPI, a fresh IPI is issued to read and cache the values again. This minimizes the number of IPIs required to be sent when these values are read back-to-back via the sysfs interface. Test-results: While reading the four sysfs files back-to-back for a given CPU every second for 100 seconds. Without patch 6/6 (Without caching): 16 [XICS 2 Edge IPI] = 422 times DBL [Doorbell interrupts] = 13 times Total : 435 IPIs. With patch 6/6 (With caching): 16 [XICS 2 Edge IPI] = 111 times DBL [Doorbell interrupts] = 17 times Total : 128 IPIs. Motivation: =========== On PSeries LPARs, the data centers planners desire a more accurate view of system utilization per resource such as CPU to plan the system capacity requirements better. Such accuracy can be obtained by reading PURR/SPURR registers for CPU resource utilization. Tools such as lparstat which are used to compute the utilization need to know [S]PURR ticks when the cpu was busy or idle. The [S]PURR counters are already exposed through sysfs. We already account for PURR ticks when we go to idle so that we can update the VPA area. This patchset extends support to account for SPURR ticks when idle, and expose both via per-cpu sysfs files. These patches are required for enhancement to the lparstat utility that compute the CPU utilization based on PURR and SPURR which can be found here : https://groups.google.com/forum/#!topic/powerpc-utils-devel/fYRo69xO9r4 With the patches, when lparstat is run on a LPAR running CPU-Hogs, ========================================================================= sudo ./src/lparstat -E 1 3 System Configuration type=Dedicated mode=Capped smt=8 lcpu=2 mem=4834176 kB cpus=0 ent=2.00 ---Actual--- -Normalized- %busy %idle Frequency %busy %idle ------ ------ ------------- ------ ------ 1 99.99 0.00 3.35GHz[111%] 110.99 0.00 2 100.00 0.00 3.35GHz[111%] 111.00 0.00 3 100.00 0.00 3.35GHz[111%] 111.00 0.00 ========================================================================= When lparstat is run on an LPAR that is idle, ========================================================================= $ sudo ./src/lparstat -E 1 3 System Configuration type=Dedicated mode=Capped smt=8 lcpu=2 mem=4834176 kB cpus=0 ent=2.00 ---Actual--- -Normalized- %busy %idle Frequency %busy %idle ------ ------ ------------- ------ ------ 1 0.71 99.30 2.18GHz[ 72%] 0.53 71.48 2 0.56 99.44 2.11GHz[ 70%] 0.43 69.57 3 0.54 99.46 2.11GHz[ 70%] 0.43 69.57 ========================================================================= Gautham R. Shenoy (6): powerpc: Move idle_loop_prolog()/epilog() functions to header file powerpc/idle: Add accessor function to always read latest idle PURR powerpc/pseries: Account for SPURR ticks on idle CPUs powerpc/sysfs: Show idle_purr and idle_spurr for every CPU Documentation: Document sysfs interfaces purr, spurr, idle_purr, idle_spurr pseries/sysfs: Minimise IPI noise while reading [idle_][s]purr Documentation/ABI/testing/sysfs-devices-system-cpu | 39 ++++++ arch/powerpc/include/asm/idle.h | 89 ++++++++++++++ arch/powerpc/kernel/sysfs.c | 133 +++++++++++++++++++-- arch/powerpc/platforms/pseries/setup.c | 8 +- drivers/cpuidle/cpuidle-pseries.c | 39 ++---- 5 files changed, 267 insertions(+), 41 deletions(-) create mode 100644 arch/powerpc/include/asm/idle.h -- 1.9.4
