linux-kernel - Re: [RFC PATCH] sched: smart wake-affine

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Date:	Mon, 03 Jun 2013 08:05:14 +0200
From:	Mike Galbraith <efault@....de>
To:	Michael Wang <wangyun@...ux.vnet.ibm.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Alex Shi <alex.shi@...el.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Turner <pjt@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>,
	Ram Pai <linuxram@...ibm.com>
Subject: Re: [RFC PATCH] sched: smart wake-affine

On Mon, 2013-06-03 at 13:50 +0800, Michael Wang wrote: 
> On 06/03/2013 01:22 PM, Mike Galbraith wrote:
> [snip]
> >>
> >> I agree that this idea, in other work, 'stop wake-affine when current is
> >> busy with wakeup' may miss the chance to bring benefit, although I could
> >> not find such workload, but I can't do promise...
> > 
> > Someday we'll find the perfect balance... likely the day before the sun
> > turns into a red giant and melts the earth.
> 
> Won't take so long ;-)
> 
> I would like to stop the regression on pgbench firstly, as PeterZ
> mentioned, if someone reported other regressions, we will know what is
> missing, if fix is possible, we fix it, if cost is too high, then I say
> we ignore the illegal income, after all, we could not benefit one in the
> cost of sacrifice others...
> 
> I'd like to fix the problem ASAP, it's really a big, urgent problem on
> my point of view, but doesn't win enough attentions as I thought it will...

I fully agree that it's a problem, but not that it's a regression.  The
"we became too buddy-centric" problem has existed for a long time, it's
just that pgbench in 1:N mode shows us how much that pull pull pull can
cost us in scalability.

A much more interesting pgbench test (imho) would be with one server per
socket.  1 server (mother of all work) driving a multi-socket sized load
is just silly, can't possibly scale, so it's important that improving
1:N pgbench (we can, and need to) doesn't harm sane loads.

-Mike

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