Date:	Mon, 03 Nov 2014 10:12:28 +0800
From:	Wanpeng Li <kernellwp@...il.com>
To:	Vincent Guittot <vincent.guittot@...aro.org>, peterz@...radead.org,
	mingo@...nel.org, linux-kernel@...r.kernel.org,
	preeti@...ux.vnet.ibm.com, Morten.Rasmussen@....com,
	kamalesh@...ux.vnet.ibm.com, linux@....linux.org.uk,
	linux-arm-kernel@...ts.infradead.org
CC:	riel@...hat.com, efault@....de, nicolas.pitre@...aro.org,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH v8 00/10] sched: consolidation of CPU capacity and usage

Hi Vincent,
On 14/10/31 下午4:47, 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

I don't know the history, could you explain what's the meaning of 'ghost 
cores' ?

Regards,
Wanpeng Li

> 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 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 (8):
>    sched: add per rq cpu_capacity_orig
>    sched: remove frequency scaling from cpu_capacity
>    sched: move cfs task on a CPU with higher capacity
>    sched: add utilization_avg_contrib
>    sched: get CPU's usage statistic
>    sched: replace capacity_factor by usage
>    sched: add SD_PREFER_SIBLING for SMT level
>    sched: make scale_rt invariant with frequency
>
>   include/linux/sched.h |  21 ++-
>   kernel/sched/core.c   |  15 +-
>   kernel/sched/debug.c  |  12 +-
>   kernel/sched/fair.c   | 369 ++++++++++++++++++++++++++++++++------------------
>   kernel/sched/sched.h  |  15 +-
>   5 files changed, 276 insertions(+), 156 deletions(-)
>

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