Date: Fri, 3 Aug 2007 13:10:13 -0700
From: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
To: Nick Piggin <npiggin@suse.de>
Cc: Martin Bligh <mbligh@mbligh.org>,
       Lee Schermerhorn <Lee.Schermerhorn@hp.com>, Andi Kleen <ak@suse.de>,
       Ingo Molnar <mingo@elte.hu>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Linux Memory Management List <linux-mm@kvack.org>,
       Eric Whitney <eric.whitney@hp.com>
Subject: Re: [rfc] balance-on-fork NUMA placement
Message-ID: <20070803201013.GA12874@linux-os.sc.intel.com>
References: <20070731054142.GB11306@wotan.suse.de> <200707311114.09284.ak@suse.de> <20070801002313.GC31006@wotan.suse.de> <46B0C8A3.8090506@mbligh.org> <1185993169.5059.79.camel@localhost> <46B10E9B.2030907@mbligh.org> <20070802013631.GA15595@wotan.suse.de> <46B22383.5020109@mbligh.org> <20070803002010.GB14775@wotan.suse.de>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20070803002010.GB14775@wotan.suse.de>
User-Agent: Mutt/1.4.1i
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2557
Lines: 55

On Fri, Aug 03, 2007 at 02:20:10AM +0200, Nick Piggin wrote:
> On Thu, Aug 02, 2007 at 11:33:39AM -0700, Martin Bligh wrote:
> > Nick Piggin wrote:
> > >On Wed, Aug 01, 2007 at 03:52:11PM -0700, Martin Bligh wrote:
> > >>>And so forth.  Initial forks will balance.  If the children refuse to
> > >>>die, forks will continue to balance.  If the parent starts seeing short
> > >>>lived children, fork()s will eventually start to stay local.  
> > >>Fork without exec is much more rare than without. Optimising for
> > >>the uncommon case is the Wrong Thing to Do (tm). What we decided
> > >
> > >It's only the wrong thing to do if it hurts the common case too
> > >much. Considering we _already_ balance on exec, then adding another
> > >balance on fork is not going to introduce some order of magnitude
> > >problem -- at worst it would be 2x but it really isn't too slow
> > >anyway (at least nobody complained when we added it).
> > >
> > >One place where we found it helps is clone for threads.
> > >
> > >If we didn't do such a bad job at keeping tasks together with their
> > >local memory, then we might indeed reduce some of the balance-on-crap
> > >and increase the aggressiveness of periodic balancing.
> > >
> > >Considering we _already_ balance on fork/clone, I don't know what
> > >your argument is against this patch is? Doing the balance earlier
> > >and allocating more stuff on the local node is surely not a bad
> > >idea.
> > 
> > I don't know who turned that on ;-( I suspect nobody bothered
> > actually measuring it at the time though, or used some crap
> > benchmark like stream to do so. It should get reverted.
> 
> So you have numbers to show it hurts? I tested some things where it
> is not supposed to help, and it didn't make any difference. Nobody
> else noticed either.
> 
> If the cost of doing the double balance is _really_ that painful,
> then we ccould skip balance-on-exec for domains with balance-on-fork
> set.

Nick, Even if it is not painful, can we skip balance-on-exec if
balance-on-fork is set. There is no need for double balance, right?

Especially with the optimization you are trying to do with this patch,
balance-on-exec may lead to wrong decision making this optimization
not work as expected.

or perhaps do balance-on-fork based on clone_flags..

thanks,
suresh
-
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/