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From: Mel Gorman <mgorman@techsingularity.net>
To: Aubrey Li <aubrey.li@linux.intel.com>
Cc: Barry Song <21cnbao@gmail.com>,
	linux-kernel@vger.kernel.org, mingo@kernel.org,
	peterz@infradead.org, song.bao.hua@hisilicon.com,
	valentin.schneider@arm.com, vincent.guittot@linaro.org,
	yangyicong@huawei.com
Subject: Re: [PATCH 8/9] sched/fair: select idle cpu from idle cpumask for task wakeup
Date: Fri, 17 Sep 2021 14:35:12 +0100	[thread overview]
Message-ID: <20210917133512.GH3959@techsingularity.net> (raw)
In-Reply-To: <865702ea-b1c1-e39d-94ea-d55bf03b86db@linux.intel.com>

On Fri, Sep 17, 2021 at 05:11:11PM +0800, Aubrey Li wrote:
> On 9/17/21 12:15 PM, Barry Song wrote:
> >> @@ -4965,6 +4965,7 @@ void scheduler_tick(void)
> >>
> >>  #ifdef CONFIG_SMP
> >> 	rq->idle_balance = idle_cpu(cpu);
> >> +	update_idle_cpumask(cpu, rq->idle_balance);
> >>  	trigger_load_balance(rq);
> >>  #endif
> >> }
> > 
> > might be stupid, a question bothering yicong and me is that why don't we
> > choose to update_idle_cpumask() while idle task exits and switches to a
> > normal task?
> 
> I implemented that way and we discussed before(RFC v1 ?), updating a cpumask
> at every enter/exit idle is more expensive than we expected, though it's
> per LLC domain, Vincent saw a significant regression IIRC. You can also
> take a look at nohz.idle_cpus_mask as a reference.
> 

It's possible to track it differently and I prototyped it some time
back. The results were mixed at the time. It helped some workloads
and was marginal on others. It appeared to help hackbench but I found
that hackbench is much more vulnerable to the wakeup_granularity and
overscheduling. For hackbench, it makes more sense to target that directly
before revisiting the alt-idlecore to see what it really helps. I'm waiting
on test results on various ways wakeup_gran can be scaled depending on
rq activity.

For alternative idle core tracking, the current 5.15-rc1 rebase
prototype looks like this

https://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git/commit/?h=sched-altidlecore-v2r8&id=b2af1a88245f6cbeb28343e89f3183a77b29d52d

Test results still pending and as usual the queue is busy. I swear, my
primary bottleneck for doing anything is benchmark and validation :(

-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2021-09-17 13:36 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-26 10:22 [RFC PATCH 0/9] Modify and/or delete SIS_PROP Mel Gorman
2021-07-26 10:22 ` [PATCH 1/9] sched/fair: Track efficiency of select_idle_sibling Mel Gorman
2021-07-26 10:22 ` [PATCH 2/9] sched/fair: Track efficiency of task recent_used_cpu Mel Gorman
2021-07-26 10:22 ` [PATCH 3/9] sched/fair: Track efficiency of select_idle_core Mel Gorman
2021-07-26 10:22 ` [PATCH 4/9] sched/fair: Use prev instead of new target as recent_used_cpu Mel Gorman
2021-07-26 10:22 ` [PATCH 5/9] sched/fair: Avoid a second scan of target in select_idle_cpu Mel Gorman
2021-07-26 10:22 ` [PATCH 6/9] sched/fair: Make select_idle_cpu() proportional to cores Mel Gorman
2021-07-26 10:22 ` [PATCH 7/9] sched/fair: Enforce proportional scan limits when scanning for an idle core Mel Gorman
2021-08-02 10:52   ` Song Bao Hua (Barry Song)
2021-08-04 10:22     ` Mel Gorman
2021-07-26 10:22 ` [PATCH 8/9] sched/fair: select idle cpu from idle cpumask for task wakeup Mel Gorman
2021-08-02 10:41   ` Song Bao Hua (Barry Song)
2021-08-04 10:26     ` Mel Gorman
2021-08-05  0:23       ` Aubrey Li
2021-09-17  3:44         ` Barry Song
2021-09-17  4:15         ` Barry Song
2021-09-17  9:11           ` Aubrey Li
2021-09-17 13:35             ` Mel Gorman [this message]
2021-07-26 10:22 ` [PATCH 9/9] sched/core: Delete SIS_PROP and rely on the idle cpu mask Mel Gorman

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