From mboxrd@z Thu Jan  1 00:00:00 1970
From: Quentin Perret <quentin.perret@arm.com>
Subject: Re: [PATCH v5 09/14] sched: Add over-utilization/tipping point
 indicator
Date: Thu, 2 Aug 2018 14:03:38 +0100
Message-ID: <20180802130337.uf6tlac2hg4nkbwr@queper01-lin>
References: <20180724122521.22109-1-quentin.perret@arm.com>
 <20180724122521.22109-10-quentin.perret@arm.com>
 <20180802122629.GU2476@hirez.programming.kicks-ass.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-kernel-owner@vger.kernel.org>
Content-Disposition: inline
In-Reply-To: <20180802122629.GU2476@hirez.programming.kicks-ass.net>
Sender: linux-kernel-owner@vger.kernel.org
To: Peter Zijlstra <peterz@infradead.org>
Cc: rjw@rjwysocki.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, gregkh@linuxfoundation.org, mingo@redhat.com, dietmar.eggemann@arm.com, morten.rasmussen@arm.com, chris.redpath@arm.com, patrick.bellasi@arm.com, valentin.schneider@arm.com, vincent.guittot@linaro.org, thara.gopinath@linaro.org, viresh.kumar@linaro.org, tkjos@google.com, joel@joelfernandes.org, smuckle@google.com, adharmap@quicinc.com, skannan@quicinc.com, pkondeti@codeaurora.org, juri.lelli@redhat.com, edubezval@gmail.com, srinivas.pandruvada@linux.intel.com, currojerez@riseup.net, javi.merino@kernel.org
List-Id: linux-pm@vger.kernel.org

On Thursday 02 Aug 2018 at 14:26:29 (+0200), Peter Zijlstra wrote:
> On Tue, Jul 24, 2018 at 01:25:16PM +0100, Quentin Perret wrote:
> > @@ -5100,8 +5118,17 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> >  		update_cfs_group(se);
> >  	}
> >  
> > -	if (!se)
> > +	if (!se) {
> >  		add_nr_running(rq, 1);
> > +		/*
> > +		 * The utilization of a new task is 'wrong' so wait for it
> > +		 * to build some utilization history before trying to detect
> > +		 * the overutilized flag.
> > +		 */
> > +		if (flags & ENQUEUE_WAKEUP)
> > +			update_overutilized_status(rq);
> > +
> > +	}
> >  
> >  	hrtick_update(rq);
> >  }
> 
> That is a somewhat dodgy hack. There is no guarantee what so ever that
> when the task wakes next its history is any better. The comment doesn't
> reflect this I feel.

AFAICT the main use-case here is to avoid re-enabling the load balance
and ruining all the task placement because of a tiny task. I don't
really see how we can do that differently ...

Or am I missing something Morten ?

In the meantime, I can try to improve the comment at least :-)

Thanks,
Quentin