Re: [PATCH v10 00/11] sched: consolidation of CPU capacity and usage

From: Wanpeng Li
Date: Wed Apr 01 2015 - 22:05:23 EST

Hi Vincent,
On Fri, Feb 27, 2015 at 04:54:03PM +0100, Vincent Guittot wrote:
>This patchset consolidates several changes in the capacity and the usage
>tracking of the CPU. It provides a frequency invariant metric of the usage of
>CPUs and generally improves the accuracy of load/usage tracking in the
>scheduler. The frequency invariant metric is the foundation required for the
>consolidation of cpufreq and implementation of a fully invariant load tracking.
>These are currently WIP and require several changes to the load balancer
>(including how it will use and interprets load and capacity metrics) and
>extensive validation. The frequency invariance is done with
>arch_scale_freq_capacity and this patchset doesn't provide the backends of
>the function which are architecture dependent.
>As discussed at LPC14, Morten and I have consolidated our changes into a single
>patchset to make it easier to review and merge.
>During load balance, the scheduler evaluates the number of tasks that a group
>of CPUs can handle. The current method assumes that tasks have a fix load of
>SCHED_LOAD_SCALE and CPUs have a default capacity of SCHED_CAPACITY_SCALE.
>This assumption generates wrong decision by creating ghost cores or by
>removing real ones when the original capacity of CPUs is different from the
>default SCHED_CAPACITY_SCALE. With this patch set, we don't try anymore to
>evaluate the number of available cores based on the group_capacity but instead
>we evaluate the usage of a group and compare it with its capacity.
>This patchset mainly replaces the old capacity_factor method by a new one and
>keeps the general policy almost unchanged. These new metrics will be also used
>in later patches.
>The CPU usage is based on a running time tracking version of the current
>implementation of the load average tracking. I also have a version that is
>based on the new implementation proposal [1] but I haven't provide the patches
>and results as [1] is still under review. I can provide change above [1] to
>change how CPU usage is computed and to adapt to new mecanism.

Is there performance data for this cpu capacity and usage improvement?

Wanpeng Li

>Change since V9
> - add a dedicated patch for removing unused capacity_orig
> - update some comments and fix typo
> - change the condition for actively migrating task on CPU with higher capacity
>Change since V8
> - reorder patches
>Change since V7
> - add freq invariance for usage tracking
> - add freq invariance for scale_rt
> - update comments and commits' message
> - fix init of utilization_avg_contrib
> - fix prefer_sibling
>Change since V6
> - add group usage tracking
> - fix some commits' messages
> - minor fix like comments and argument order
>Change since V5
> - remove patches that have been merged since v5 : patches 01, 02, 03, 04, 05, 07
> - update commit log and add more details on the purpose of the patches
> - fix/remove useless code with the rebase on patchset [2]
> - remove capacity_orig in sched_group_capacity as it is not used
> - move code in the right patch
> - add some helper function to factorize code
>Change since V4
> - rebase to manage conflicts with changes in selection of busiest group
>Change since V3:
> - add usage_avg_contrib statistic which sums the running time of tasks on a rq
> - use usage_avg_contrib instead of runnable_avg_sum for cpu_utilization
> - fix replacement power by capacity
> - update some comments
>Change since V2:
> - rebase on top of capacity renaming
> - fix wake_affine statistic update
> - rework nohz_kick_needed
> - optimize the active migration of a task from CPU with reduced capacity
> - rename group_activity by group_utilization and remove unused total_utilization
> - repair SD_PREFER_SIBLING and use it for SMT level
> - reorder patchset to gather patches with same topics
>Change since V1:
> - add 3 fixes
> - correct some commit messages
> - replace capacity computation by activity
> - take into account current cpu capacity
>Morten Rasmussen (2):
> sched: Track group sched_entity usage contributions
> sched: Make sched entity usage tracking scale-invariant
>Vincent Guittot (9):
> sched: add utilization_avg_contrib
> sched: remove frequency scaling from cpu_capacity
> sched: make scale_rt invariant with frequency
> sched: add per rq cpu_capacity_orig
> sched: get CPU's usage statistic
> sched: replace capacity_factor by usage
> sched; remove unused capacity_orig from
> sched: add SD_PREFER_SIBLING for SMT level
> sched: move cfs task on a CPU with higher capacity
> include/linux/sched.h | 21 ++-
> kernel/sched/core.c | 15 +--
> kernel/sched/debug.c | 12 +-
> kernel/sched/fair.c | 366 +++++++++++++++++++++++++++++++-------------------
> kernel/sched/sched.h | 15 ++-
> 5 files changed, 271 insertions(+), 158 deletions(-)
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