Message-ID: <1370236944.5988.108.camel@marge.simpson.net>
Subject: Re: [RFC PATCH] sched: smart wake-affine
From: Mike Galbraith <efault@gmx.de>
To: Michael Wang <wangyun@linux.vnet.ibm.com>
Cc: LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, Alex Shi <alex.shi@intel.com>,
        Namhyung Kim <namhyung@kernel.org>, Paul Turner <pjt@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        "Nikunj A. Dadhania" <nikunj@linux.vnet.ibm.com>,
        Ram Pai <linuxram@us.ibm.com>
Date: Mon, 03 Jun 2013 07:22:24 +0200
In-Reply-To: <51AC2121.1060903@linux.vnet.ibm.com>
References: <51A43B16.9080801@linux.vnet.ibm.com>
	 <51ABFF6A.60206@linux.vnet.ibm.com>
	 <1370228941.5988.66.camel@marge.simpson.net>
	 <51AC0CD4.9070302@linux.vnet.ibm.com>
	 <1370231597.5988.79.camel@marge.simpson.net>
	 <51AC2121.1060903@linux.vnet.ibm.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
Mime-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2841
Lines: 69

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

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/