linux-kernel - Re: [PATCH v4] sched/core: Preempt current task in favour of bound kthread

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Message-Id: <20191213053200.GA18602@linux.vnet.ibm.com>
Date:   Fri, 13 Dec 2019 11:02:00 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Dave Chinner <david@...morbit.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

* Peter Zijlstra <peterz@...radead.org> [2019-12-12 11:10:31]:

> On Thu, Dec 12, 2019 at 09:46:17AM +1100, Dave Chinner wrote:
> > On Wed, Dec 11, 2019 at 11:08:29PM +0530, Srikar Dronamraju wrote:
> 
> Good point, something to maybe try (Srikar?) is making tick preemption
> more agressive for such tasks.
> 
> The below extends the previous patch to retain the set_next_buddy() on
> wakeup, but does not make the actual preemption more agressive.
> 
> Then it 'fixes' the tick preemption to better align with the actual
> scheduler pick (ie. consider the buddy hints).
> 

Just to let you know, I tried the patch, but it doesn't help.
The results were identical to the one without the patch.

I think its probably because when we allow the task to stay on the runqueue,
it will surely lead to load_balance and so we see the active-balance kick
in.

Peter, Based on what Dave is asking for, would you be okay if we add

1. A delayed_wake_list per runqueue,
2. A new wake_up API to add tasks to this delayed wake_list
3. On schedule, tasks on the delayed_wake_list would be actually woken up.

-- 
Thanks and Regards
Srikar Dronamraju