linux-kernel - Re: [PATCH] sched/fair: don't assign runtime for throttled cfs

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Message-ID: <ce1b05b1-d4d3-140e-b611-0482fa9fd3f5@arm.com>
Date:   Fri, 16 Aug 2019 18:19:41 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Liangyan <liangyan.peng@...ux.alibaba.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, shanpeic@...ux.alibaba.com,
        xlpang@...ux.alibaba.com, pjt@...gle.com
Subject: Re: [PATCH] sched/fair: don't assign runtime for throttled cfs_rq

On 16/08/2019 16:39, Liangyan wrote:
> Thanks for the feedback.
> Add some debug prints and get below log. It seems that pick_next_task_fair throttle the cfs_rq first, then call put_prev_entity to assign runtime to this cfs_rq.
> 
[...]
> 
> Regarding the suggested change,  i’m not  sure whether it is ok to skip the runtime account for curr task.
> 

Yeah it's probably pretty stupid. IIRC throttled cfs_rq means frozen
rq_clock, so any subsequent call to update_curr() on a throttled cfs_rq
should lead to an early bailout anyway due to delta_exec <= 0.