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

[Vincent Guittot <vincent.guittot@linaro.org>]

On 27 February 2015 at 16:54, Vincent Guittot
<vincent.guittot@linaro.org> 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.
>
> 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
>
> [1] https://lkml.org/lkml/2014/10/10/131
> [2] https://lkml.org/lkml/2014/7/25/589
>
> 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(-)
>
> --
> 1.9.1
>

Hi Peter,

Gentle reminder ping