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Subject: Re: [PATCH 2/3] sched,fair: Fix local starvation
From: Mike Galbraith <mgalbraith@suse.de>
To: Peter Zijlstra <peterz@infradead.org>, mingo@kernel.org,
        linux-kernel@vger.kernel.org
Cc: Pavan Kondeti <pkondeti@codeaurora.org>, Ben Segall <bsegall@google.com>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Paul Turner <pjt@google.com>, Thomas Gleixner <tglx@linutronix.de>,
        byungchul.park@lge.com, Andrew Hunter <ahh@google.com>
Date: Sat, 21 May 2016 16:04:48 +0200
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	 <20160510174613.902178264@infradead.org>
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On Tue, 2016-05-10 at 19:43 +0200, Peter Zijlstra wrote:

(Evolution authors must either not do patch review, or use some other
mailer.  Squint hard, this crud really is your patch;)

> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
>  
> @@ -1762,7 +1770,11 @@ void sched_ttwu_pending(void)
>  > 	> while (llist) {
>  > 	> 	> p = llist_entry(llist, struct task_struct, wake_entry);
>  > 	> 	> llist = llist_next(llist);
> -> 	> 	> ttwu_do_activate(rq, p, 0, cookie);
> +> 	> 	> /*
> +> 	> 	>  * See ttwu_queue(); we only call ttwu_queue_remote() when
> +> 	> 	>  * its a x-cpu wakeup.
> +> 	> 	>  */
> +> 	> 	> ttwu_do_activate(rq, p, WF_MIGRATED, cookie);

Wakees that were not migrated/normalized eat an unwanted min_vruntime,
and likely take a size XXL latency hit.  Big box running master bled
profusely under heavy load until I turned TTWU_QUEUE off.

	-Mike