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

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Date:	Mon, 03 Jun 2013 07:22:24 +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 12:52 +0800, Michael Wang wrote: 
> On 06/03/2013 11:53 AM, Mike Galbraith wrote:
> > On Mon, 2013-06-03 at 11:26 +0800, Michael Wang wrote: 
> >> On 06/03/2013 11:09 AM, Mike Galbraith wrote:
> >>> On Mon, 2013-06-03 at 10:28 +0800, Michael Wang wrote: 
> >>>> On 05/28/2013 01:05 PM, Michael Wang wrote:
> >>>>> wake-affine stuff is always trying to pull wakee close to waker, by theory,
> >>>>> this will bring benefit if waker's cpu cached hot data for wakee, or the
> >>>>> extreme ping-pong case.
> >>>>>
> >>>>> And testing show it could benefit hackbench 15% at most.
> >>>>>
> >>>>> However, the whole stuff is somewhat blindly and time-consuming, some
> >>>>> workload therefore suffer.
> >>>>>
> >>>>> And testing show it could damage pgbench 50% at most.
> >>>>>
> >>>>> Thus, wake-affine stuff should be smarter, and realise when to stop
> >>>>> it's thankless effort.
> >>>>
> >>>> Is there any comments?
> >>>
> >>> (I haven't had time to test-drive yet, -rt munches time like popcorn)
> >>
> >> I see ;-)
> >>
> >> During my testing, this one works well on the box, solved the issues of
> >> pgbench and won't harm hackbench any, I think we have caught some good
> >> point here :)
> > 
> > Some wider spectrum testing needs doing though.
> 
> That's right, the benchmark I currently have is hackbench, pgbench,
> ebizzy, aim7, tbench, dbench, kbench, is there any other good candidate
> we should add to the test?

pgsql/mysql+oltp are useful.  I used to track mysql especially all the
time, until I lost my fast mysql database, and couldn't re-create
anything that wasn't a complete slug.

> Hackbench is a good
> > sign, but localhost and db type stuff that really suffer from misses
> > would be good to test.  Java crud tends to be sensitive too.  I used to
> > watch vmark (crap) as an indicator,
> 
> I can't get it from google...do you mean vmmark?

No, crusty old, and widely disparaged as being a useless POS benchmark,
volanomark.  The big boys do SPECjbb, maybe that's better quality java
crud, dunno, never had it to play with.

> if you see unhappiness there, you'll
> > very likely see it in other loads as well, it is very fond of cache
> > affine wakeups, but loathes preemption (super heavy loads usually do).
> 
> 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.

-Mike

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