lkml.org 
[lkml]   [2014]   [Aug]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] sched: Reduce contention in update_cfs_rq_blocked_load
On 08/04/2014 04:28 PM, Jason Low wrote:
> When running workloads on 2+ socket systems, based on perf profiles, the
> update_cfs_rq_blocked_load function constantly shows up as taking up a
> noticeable % of run time. This is especially apparent on an 8 socket
> machine. For example, when running the AIM7 custom workload, we see:
>
> 4.18% reaim [kernel.kallsyms] [k] update_cfs_rq_blocked_load
>
> Much of the contention is in __update_cfs_rq_tg_load_contrib when we
> update the tg load contribution stats. However, it turns out that in many
> cases, they don't need to be updated and "tg_contrib" is 0.
>
> This patch adds a check in __update_cfs_rq_tg_load_contrib to skip updating
> tg load contribution stats when nothing needs to be updated. This reduces the
> cacheline contention that would be unnecessary. In the above case, with the
> patch, perf reports the total time spent in this function went down by more
> than a factor of 3x:
>
> 1.18% reaim [kernel.kallsyms] [k] update_cfs_rq_blocked_load
>
> Signed-off-by: Jason Low<jason.low2@hp.com>
> ---
> kernel/sched/fair.c | 3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index bfa3c86..8d4cc72 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -2377,6 +2377,9 @@ static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
> tg_contrib = cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg;
> tg_contrib -= cfs_rq->tg_load_contrib;
>
> + if (!tg_contrib)
> + return;
> +
> if (force_update || abs(tg_contrib)> cfs_rq->tg_load_contrib / 8) {
> atomic_long_add(tg_contrib,&tg->load_avg);
> cfs_rq->tg_load_contrib += tg_contrib;
Reviewed-by: Waiman Long <Waiman.Long@hp.com>



\
 
 \ /
  Last update: 2014-08-05 20:21    [W:0.333 / U:0.220 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site