linux-kernel - Re: [PATCH 1/2] sched/fair: Couple wakee flips with heavy wakers

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Date:   Tue, 09 Nov 2021 13:55:24 +0100
From:   Mike Galbraith <efault@....de>
To:     Peter Zijlstra <peterz@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Valentin Schneider <valentin.schneider@....com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Barry Song <song.bao.hua@...ilicon.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched/fair: Couple wakee flips with heavy wakers

On Tue, 2021-11-09 at 12:56 +0100, Peter Zijlstra wrote:
> 
> 
> > @@ -5895,7 +5903,7 @@ static int wake_wide(struct task_struct *p)
> >  
> >         if (master < slave)
> >                 swap(master, slave);
> > -       if (slave < factor || master < slave * factor)
> > +       if ((slave < factor && master < (factor>>1)*factor) || master < slave * factor)
> >                 return 0;
> >         return 1;
> >  }
> 
> has factor.
> 
> Now:
> 
>         !(slave < factor || master < slave * factor)
> 
>   !(x || y) == !x && !y, gives:
> 
>         slave >= factor && master >= slave * factor
> 
>   subst lhr in rhs:
> 
>         master >= factor * factor
> 
> 
> your extra term:
> 
>         !((slave < factor && master < (factor*factor)/2) || master < slave * factor)
> 
> changes that how? AFAICT it's a nop.

That can happen when twiddling.  The thought was to let volume on the
right override individual thread decay on the left to a limited extent.

	-Mike