linux-kernel - Re: [patch] sched: beef up wake

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Date:	Thu, 09 Jul 2015 16:46:09 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Josef Bacik <jbacik@...com>, riel@...hat.com, mingo@...hat.com,
	linux-kernel@...r.kernel.org, morten.rasmussen@....com,
	kernel-team <Kernel-team@...com>
Subject: Re: [patch] sched: beef up wake_wide()

On Thu, 2015-07-09 at 16:07 +0200, Mike Galbraith wrote:
> On Thu, 2015-07-09 at 15:26 +0200, Peter Zijlstra wrote:
> > On Wed, Jul 08, 2015 at 08:13:46AM +0200, Mike Galbraith wrote:
> > > 
> > > +/*
> > > + * Detect 1:N waker/wakee relationship via a switching-frequency heuristic.
> > > + * A waker of many should wake a different task than the one last awakened
> > > + * at a frequency roughly N times higher than one of its wakees.  In order
> > > + * to determine whether we should let the load spread vs consolodating to
> > > + * shared cache, we look for a minimum 'flip' frequency of llc_size in one
> > > + * partner, and a factor of lls_size higher frequency in the other.  With
> > > + * both conditions met, we can be relatively sure that we are seeing a 1:N
> > > + * relationship, and that load size exceeds socket size.
> > > + */
> > >  static int wake_wide(struct task_struct *p)
> > >  {
> > > +	unsigned int waker_flips = current->wakee_flips;
> > > +	unsigned int wakee_flips = p->wakee_flips;
> > >  	int factor = this_cpu_read(sd_llc_size);
> > >  
> > > +	if (waker_flips < wakee_flips)
> > > +		swap(waker_flips, wakee_flips);
> > 
> > This makes the wakee/waker names useless, the end result is more like
> > wakee_flips := client_flips, waker_flips := server_flips.
> 
> True, perhaps a rename is in order.

I should perhaps add that waker/wakee_flips does make sense to me in the
sense that the task who's flips end up in the waker_flips bucket is our
waker of many vs being one its many wakees.

	-Mike

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