From: Aubrey Li <aubrey.li@linux.intel.com>
To: "Gautham R. Shenoy" <gautham.shenoy@amd.com>,
Abel Wu <wuyun.abel@bytedance.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
linux-kernel@vger.kernel.org, srikar@linux.vnet.ibm.com,
aubrey.li@intel.com
Subject: Re: [RFC PATCH 1/5] sched/fair: record overloaded cpus
Date: Sun, 27 Feb 2022 16:08:12 +0800 [thread overview]
Message-ID: <a87fbf3b-c488-73cc-470f-09b3e2f63bd3@linux.intel.com> (raw)
In-Reply-To: <YhcvUV/jW7yr0Sn+@BLR-5CG11610CF.amd.com>
On 2/24/22 3:10 PM, Gautham R. Shenoy wrote:
> Hello Abel,
>
> (+ Aubrey Li, Srikar)
>
> On Thu, Feb 17, 2022 at 11:43:57PM +0800, Abel Wu wrote:
>> An CFS runqueue is considered overloaded when there are
>> more than one pullable non-idle tasks on it (since sched-
>> idle cpus are treated as idle cpus). And idle tasks are
>> counted towards rq->cfs.idle_h_nr_running, that is either
>> assigned SCHED_IDLE policy or placed under idle cgroups.
>>
>> The overloaded cfs rqs can cause performance issues to
>> both task types:
>>
>> - for latency critical tasks like SCHED_NORMAL,
>> time of waiting in the rq will increase and
>> result in higher pct99 latency, and
>>
>> - batch tasks may not be able to make full use
>> of cpu capacity if sched-idle rq exists, thus
>> presents poorer throughput.
>>
>> The mask of overloaded cpus is updated in periodic tick
>> and the idle path at the LLC domain basis. This cpumask
>> will also be used in SIS as a filter, improving idle cpu
>> searching.
>
> This is an interesting approach to minimise the tail latencies by
> keeping track of the overloaded cpus in the LLC so that
> idle/sched-idle CPUs can pull from them. This approach contrasts with the
> following approaches that were previously tried :
>
> 1. Maintain the idle cpumask at the LLC level by Aubrey Li
> https://lore.kernel.org/all/1615872606-56087-1-git-send-email-aubrey.li@intel.com/
>
> 2. Maintain the identity of the idle core itself at the LLC level, by Srikar :
> https://lore.kernel.org/lkml/20210513074027.543926-3-srikar@linux.vnet.ibm.com/
>
> There have been concerns in the past about having to update the shared
> mask/counter at regular intervals. Srikar, Aubrey any thoughts on this
> ?
>
https://lkml.org/lkml/2022/2/7/1129
next prev parent reply other threads:[~2022-02-27 8:08 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-17 15:43 [RFC PATCH 0/5] introduce sched-idle balancing Abel Wu
2022-02-17 15:43 ` [RFC PATCH 1/5] sched/fair: record overloaded cpus Abel Wu
2022-02-24 7:10 ` Gautham R. Shenoy
2022-02-24 14:36 ` Abel Wu
2022-02-27 8:08 ` Aubrey Li [this message]
2022-02-17 15:43 ` [RFC PATCH 2/5] sched/fair: introduce sched-idle balance Abel Wu
2022-02-17 15:43 ` [RFC PATCH 3/5] sched/fair: add stats for sched-idle balancing Abel Wu
2022-02-17 15:44 ` [RFC PATCH 4/5] sched/fair: filter out overloaded cpus in sis Abel Wu
2022-02-17 15:44 ` [RFC PATCH 5/5] sched/fair: favor cpu capacity for idle tasks Abel Wu
2022-02-24 3:19 ` [RFC PATCH 0/5] introduce sched-idle balancing Abel Wu
2022-02-24 15:20 ` Peter Zijlstra
2022-02-24 15:29 ` Vincent Guittot
2022-02-25 6:51 ` Abel Wu
2022-02-25 6:46 ` Abel Wu
2022-02-25 8:29 ` Vincent Guittot
2022-02-25 10:46 ` Abel Wu
2022-02-25 13:15 ` Vincent Guittot
2022-02-24 16:47 ` Mel Gorman
2022-02-25 8:15 ` Abel Wu
2022-02-25 10:16 ` Mel Gorman
2022-02-25 13:20 ` Abel Wu
2022-03-02 0:41 ` Josh Don
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