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Date: Thu, 12 Dec 2019 11:14:24 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Dave Chinner <david@...morbit.com>
Cc: Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Phil Auld <pauld@...hat.com>, Ming Lei <ming.lei@...hat.com>,
linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org,
Jeff Moyer <jmoyer@...hat.com>,
Dave Chinner <dchinner@...hat.com>,
Eric Sandeen <sandeen@...hat.com>,
Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
Ingo Molnar <mingo@...hat.com>, Tejun Heo <tj@...nel.org>,
Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH v4] sched/core: Preempt current task in favour of bound
kthread
On Thu, Dec 12, 2019 at 11:10:31AM +0100, Peter Zijlstra wrote:
> @@ -4156,13 +4159,13 @@ check_preempt_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr)
> if (delta_exec < sysctl_sched_min_granularity)
> return;
>
> - se = __pick_first_entity(cfs_rq);
> + se = __pick_next_entity(cfs_rq, NULL);
> delta = curr->vruntime - se->vruntime;
>
> if (delta < 0)
> return;
What I mean with the below comment is, when this isn't enough, try
something like:
if (se == cfs_rq->next)
ideal_runtime /= 2;
to make it yield sooner to 'next' buddies. Sadly, due to the whole
cgroup mess, we can't say what actual task is on the end of it (without
doing a full hierarchy pick, which is more expensive still).
> - if (delta > ideal_runtime)
> + if (delta > ideal_runtime) // maybe frob this too ?
> resched_curr(rq_of(cfs_rq));
> }
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