linux-kernel - Re: [PATCH 1/6] sched: Fix ttwu_queue

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Date:   Mon, 22 Jun 2020 10:11:22 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
        juri.lelli@...hat.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
        paulmck@...nel.org, frederic@...nel.org
Subject: Re: [PATCH 1/6] sched: Fix ttwu_queue_cond()

On Mon, Jun 15, 2020 at 02:56:55PM +0200, Peter Zijlstra wrote:
> Where the condition:
> 
>   !cpus_share_cache(smp_processor_id(), cpu)
> 
> already implies 'cpu != smp_processor_id()', because a CPU always
> shares cache with itself, the secondary condition added in commit:
> 
>   2ebb17717550 ("sched/core: Offload wakee task activation if it the wakee is descheduling")
> 
> voids that implication, resulting in attempting to do local wake-ups
> through the queue mechanism.
> 
> Fixes: 2ebb17717550 ("sched/core: Offload wakee task activation if it the wakee is descheduling")
> Reported-by: Paul E. McKenney <paulmck@...nel.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Tested-by: Paul E. McKenney <paulmck@...nel.org>

Yep, I mistakenly though this would be covered by the self-wakeup check
early in try_to_wake_up() but it is not

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs