Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262627AbUJ1B1K (ORCPT ); Wed, 27 Oct 2004 21:27:10 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262642AbUJ1B1K (ORCPT ); Wed, 27 Oct 2004 21:27:10 -0400 Received: from ozlabs.org ([203.10.76.45]:999 "EHLO ozlabs.org") by vger.kernel.org with ESMTP id S262627AbUJ1B1B (ORCPT ); Wed, 27 Oct 2004 21:27:01 -0400 Date: Thu, 28 Oct 2004 11:16:18 +1000 From: David Gibson To: Bill Davidsen Cc: Andrew Morton , James Cloos , linux-kernel@vger.kernel.org Subject: Re: MAP_SHARED bizarrely slow Message-ID: <20041028011618.GB2216@zax> Mail-Followup-To: David Gibson , Bill Davidsen , Andrew Morton , James Cloos , linux-kernel@vger.kernel.org References: <20041027010659.15ec7e90.akpm@osdl.org> <41800B12.5020405@tmr.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <41800B12.5020405@tmr.com> User-Agent: Mutt/1.5.6+20040907i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2532 Lines: 59 On Wed, Oct 27, 2004 at 04:54:42PM -0400, Bill Davidsen wrote: > Andrew Morton wrote: > >James Cloos wrote: > > > >>>>>>>"David" == David Gibson writes: > >> > >>David> http://www.ozlabs.org/people/dgibson/maptest.tar.gz > >> > >>David> On a number of machines I've tested - both ppc64 and x86 - the > >>David> SHARED version is consistently and significantly (50-100%) > >>David> slower than the PRIVATE version. > >> > >>Just gave it a test on my laptop and server. Both are p3. The > >>laptop is under heavier mem pressure; the server has just under > >>a gig with most free/cache/buff. Laptop is still running 2.6.7 > >>whereas the server is bk as of 2004-10-24. > >> > >>Buth took about 11 seconds for the private and around 30 seconds > >>for the shared tests. > >> > > > > > >I get the exact opposite, on a P4: > > > >vmm:/home/akpm/maptest> time ./mm-sharemmap > >./mm-sharemmap 10.81s user 0.05s system 100% cpu 10.855 total > >vmm:/home/akpm/maptest> time ./mm-sharemmap > >./mm-sharemmap 11.04s user 0.05s system 100% cpu 11.086 total > >vmm:/home/akpm/maptest> time ./mm-privmmap > >./mm-privmmap 26.91s user 0.02s system 100% cpu 26.903 total > >vmm:/home/akpm/maptest> time ./mm-privmmap > >./mm-privmmap 26.89s user 0.02s system 100% cpu 26.894 total > >vmm:/home/akpm/maptest> uname -a > >Linux vmm 2.6.10-rc1-mm1 #14 SMP Tue Oct 26 23:23:23 PDT 2004 i686 i686 > >i386 GNU/Linux > > > >It's all user time so I can think of no reason apart from physical page > >allocation order causing additional TLB reloads in one case. One is using > >anonymous pages and the other is using shmem-backed pages, although I can't > >think why that would make a difference. > > I think the cause was covered in another post, I'm surprised that the > page overhead is reported as user time. It would have been a good hint > if the big jump were in system time. The cause isn't page overhead. The problem is that the SHARED version actually uses a whole lot more real memory, so cache performance is much worse. So the time really is in userland. -- David Gibson | For every complex problem there is a david AT gibson.dropbear.id.au | solution which is simple, neat and | wrong. http://www.ozlabs.org/people/dgibson - 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/