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From: Tao Zhou <tao.zhou@linux.dev>
To: Mel Gorman <mgorman@techsingularity.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Aubrey Li <aubrey.li@linux.intel.com>,
	Barry Song <song.bao.hua@hisilicon.com>,
	Mike Galbraith <efault@gmx.de>,
	Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Tao Zhou <tao.zhou@linux.dev>
Subject: Re: [PATCH 1/2] sched/fair: Couple wakee flips with heavy wakers
Date: Fri, 29 Oct 2021 00:19:48 +0800	[thread overview]
Message-ID: <YXrNfHcfhp2LutiL@geo.homenetwork> (raw)
In-Reply-To: <20211028094834.1312-2-mgorman@techsingularity.net>

Hi Mel,

On Thu, Oct 28, 2021 at 10:48:33AM +0100, Mel Gorman wrote:

> @@ -5865,6 +5865,14 @@ static void record_wakee(struct task_struct *p)
>  	}
>  
>  	if (current->last_wakee != p) {
> +		int min = __this_cpu_read(sd_llc_size) << 1;
> +		/*
> +		 * Couple the wakee flips to the waker for the case where it
> +		 * doesn't accrue flips, taking care to not push the wakee
> +		 * high enough that the wake_wide() heuristic fails.
> +		 */
> +		if (current->wakee_flips > p->wakee_flips * min)
> +			p->wakee_flips++;
>  		current->last_wakee = p;
>  		current->wakee_flips++;
>  	}
> @@ -5895,7 +5903,7 @@ static int wake_wide(struct task_struct *p)
>  
>  	if (master < slave)
>  		swap(master, slave);
> -	if (slave < factor || master < slave * factor)
> +	if ((slave < factor && master < (factor>>1)*factor) || master < slave * factor)

So, the check like this include the above range:

  if ((slave < factor && master < slave * factor) ||
       master < slave * factor)

That "factor>>1" filter some.

If "slave < factor" is true and "master < (factor>>1)*factor" is false,
then we check "master < slave * factor".(This is one path added by the
check "&&  master < (factor>>1)*factor").
In the latter check "slave < factor" must be true, the result of this
check depend on slave in the range [factor, factor>>1] if there is possibility
that "master < slave * factor". If slave in [factor>>1, 0], the check of
"master < slave * factor" is absolutly false and this can be filtered if
we use a variable to load the result of master < (factor>>1)*factor.

My random random inputs and continue confusing to move on.



Thanks,
Tao

  reply	other threads:[~2021-10-28 16:19 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-28  9:48 [PATCH v4 0/2] Reduce stacking and overscheduling Mel Gorman
2021-10-28  9:48 ` [PATCH 1/2] sched/fair: Couple wakee flips with heavy wakers Mel Gorman
2021-10-28 16:19   ` Tao Zhou [this message]
2021-10-29  8:42     ` Mel Gorman
2021-11-10  9:53       ` Tao Zhou
2021-11-10 15:40         ` Mike Galbraith
2021-10-29 15:17   ` Vincent Guittot
2021-10-30  3:11     ` Mike Galbraith
2021-10-30  4:12       ` Mike Galbraith
2021-11-01  8:56     ` Mel Gorman
2021-10-28  9:48 ` [PATCH 2/2] sched/fair: Increase wakeup_gran if current task has not executed the minimum granularity Mel Gorman
2021-10-29 16:07   ` Vincent Guittot
  -- strict thread matches above, loose matches on Subject: below --
2021-10-21 14:56 [PATCH 0/2] Reduce stacking and overscheduling Mel Gorman
2021-10-21 14:56 ` [PATCH 1/2] sched/fair: Couple wakee flips with heavy wakers Mel Gorman
2021-10-22 10:26   ` Mike Galbraith
2021-10-22 11:05     ` Mel Gorman
2021-10-22 12:00       ` Mike Galbraith
2021-10-25  6:35       ` Mike Galbraith
2021-10-26  8:18         ` Mel Gorman
2021-10-26 10:15           ` Mike Galbraith
2021-10-26 10:41             ` Mike Galbraith
2021-10-26 11:57               ` Mel Gorman
2021-10-26 12:13                 ` Mike Galbraith
2021-10-27  2:09                   ` Mike Galbraith
2021-10-27  9:00                     ` Mel Gorman
2021-10-27 10:18                       ` Mike Galbraith
2021-11-09 11:56   ` Peter Zijlstra
2021-11-09 12:55     ` Mike Galbraith

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