Re: [PATCH 0/1] Reduce cost of accessing tg->load_avg

[Swapnil Sapkal <Swapnil.Sapkal@amd.com>]

Hello Aaron,

On 8/23/2023 11:38 AM, Aaron Lu wrote:
> RFC v2 -> v1:
> - drop RFC;
> - move cfs_rq->last_update_tg_load_avg before cfs_rq->tg_load_avg_contrib;
> - add Vincent's reviewed-by tag.
> 
> RFC v2:
> Nitin Tekchandani noticed some scheduler functions have high cost
> according to perf/cycles while running postgres_sysbench workload.
> I perf/annotated the high cost functions: update_cfs_group() and
> update_load_avg() and found the costs were ~90% due to accessing to
> tg->load_avg. This series is an attempt to reduce the overhead of
> the two functions.
>                                                                                                                         
> Thanks to Vincent's suggestion from v1, this revision used a simpler way
> to solve the overhead problem by limiting updates to tg->load_avg to at
> most once per ms. Benchmark shows that it has good results and with the
> rate limit in place, other optimizations in v1 don't improve performance
> further so they are dropped from this revision.
> 

I have tested this series alongside Mathieu's changes. You can find the
report here: https://lore.kernel.org/all/f6dc1652-bc39-0b12-4b6b-29a2f9cd8484@amd.com/

Tested-by: Swapnil Sapkal <Swapnil.Sapkal@amd.com>

> Aaron Lu (1):
>    sched/fair: ratelimit update to tg->load_avg
> 
>   kernel/sched/fair.c  | 13 ++++++++++++-
>   kernel/sched/sched.h |  1 +
>   2 files changed, 13 insertions(+), 1 deletion(-)
> 
--
Thanks and Regards,
Swapnil