From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756918AbZCCEm4 (ORCPT ); Mon, 2 Mar 2009 23:42:56 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752827AbZCCEmq (ORCPT ); Mon, 2 Mar 2009 23:42:46 -0500 Received: from mail.suse.de ([195.135.220.2]:42396 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751215AbZCCEmq (ORCPT ); Mon, 2 Mar 2009 23:42:46 -0500 Date: Tue, 3 Mar 2009 05:42:40 +0100 From: Nick Piggin To: Mel Gorman Cc: Lin Ming , Pekka Enberg , Linux Memory Management List , Rik van Riel , KOSAKI Motohiro , Christoph Lameter , Johannes Weiner , Linux Kernel Mailing List , Zhang Yanmin , Peter Zijlstra , Ingo Molnar Subject: Re: [RFC PATCH 00/19] Cleanup and optimise the page allocator V2 Message-ID: <20090303044239.GC3973@wotan.suse.de> References: <1235477835-14500-1-git-send-email-mel@csn.ul.ie> <1235639427.11390.11.camel@minggr> <20090226110336.GC32756@csn.ul.ie> <1235647139.16552.34.camel@penberg-laptop> <20090226112232.GE32756@csn.ul.ie> <1235724283.11610.212.camel@minggr> <20090302112122.GC21145@csn.ul.ie> <20090302113936.GJ1257@wotan.suse.de> <20090302121632.GA14217@csn.ul.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090302121632.GA14217@csn.ul.ie> User-Agent: Mutt/1.5.9i Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 02, 2009 at 12:16:33PM +0000, Mel Gorman wrote: > On Mon, Mar 02, 2009 at 12:39:36PM +0100, Nick Piggin wrote: > > > Perfect, thanks a lot for profiling this. It is a big help in figuring out > > > how the allocator is actually being used for your workloads. > > > > > > The OLTP results had the following things to say about the page allocator. > > > > Is this OLTP, or UDP-U-4K? > > > > OLTP. I didn't do a comparison for UDP due to uncertainity of what I was > looking at other than to note that high-order allocations may be a > bigger deal there. OK. > > > Question 1: Would it be possible to increase the sample rate and track cache > > > misses as well please? > > > > If the events are constantly biased, I don't think sample rate will > > help. I don't know how the internals of profiling counters work exactly, > > but you would expect yes cache misses, and stalls from any number of > > different resources could put results in funny places. > > > > Ok, if it's stalls that are the real factor then yes, increasing the > sample rate might not help. However, the same rates for instructions > were so low, I thought it might be a combination of both low sample > count and stalls happening at particular places. A profile of cache > misses will still be useful as it'll say in general if there is a marked > increase overall or not. OK. > > Intel's OLTP workload is very sensitive to cacheline footprint of the > > kernel, and if you touch some extra cachelines at point A, it can just > > result in profile hits getting distributed all over the place. Profiling > > cache misses might help, but probably see a similar phenomenon. > > > > Interesting, this might put a hole in replacing the gfp_zone() with a > version that uses an additional (or maybe two depending on alignment) > cacheline. Well... I still think it is probably a good idea. Firstly is that it probably saves a line of icache too. Secondly, I guess adding a *single* extra readonly cacheline is probably not such a problem even for this workload. I was more thinking of if you changed the pattern in which pages are allocated (ie. like the hot/cold thing), or if some change resulted in more cross-cpu operations then it could result in worse cache efficiency. But you never know, it might be one patch to look at. > > I can't remember, does your latest patchset include any patches that change > > the possible order in which pages move around? Or is it just made up of > > straight-line performance improvement of existing implementation? > > > > It shouldn't affect order. I did a test a while ago to make sure pages > were still coming back in contiguous order as some IO cards depend on this > behaviour for performance. The intention for the first pass is a straight-line > performance improvement. OK, but the dynamic behaviour too. Free page A, free page B, allocate page A allocate page B etc. The hot/cold removal would be an obvious example of what I mean, although that wasn't included in this recent patchset anyway. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id CFF646B0055 for ; Mon, 2 Mar 2009 23:42:46 -0500 (EST) Date: Tue, 3 Mar 2009 05:42:40 +0100 From: Nick Piggin Subject: Re: [RFC PATCH 00/19] Cleanup and optimise the page allocator V2 Message-ID: <20090303044239.GC3973@wotan.suse.de> References: <1235477835-14500-1-git-send-email-mel@csn.ul.ie> <1235639427.11390.11.camel@minggr> <20090226110336.GC32756@csn.ul.ie> <1235647139.16552.34.camel@penberg-laptop> <20090226112232.GE32756@csn.ul.ie> <1235724283.11610.212.camel@minggr> <20090302112122.GC21145@csn.ul.ie> <20090302113936.GJ1257@wotan.suse.de> <20090302121632.GA14217@csn.ul.ie> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090302121632.GA14217@csn.ul.ie> Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Lin Ming , Pekka Enberg , Linux Memory Management List , Rik van Riel , KOSAKI Motohiro , Christoph Lameter , Johannes Weiner , Linux Kernel Mailing List , Zhang Yanmin , Peter Zijlstra , Ingo Molnar List-ID: On Mon, Mar 02, 2009 at 12:16:33PM +0000, Mel Gorman wrote: > On Mon, Mar 02, 2009 at 12:39:36PM +0100, Nick Piggin wrote: > > > Perfect, thanks a lot for profiling this. It is a big help in figuring out > > > how the allocator is actually being used for your workloads. > > > > > > The OLTP results had the following things to say about the page allocator. > > > > Is this OLTP, or UDP-U-4K? > > > > OLTP. I didn't do a comparison for UDP due to uncertainity of what I was > looking at other than to note that high-order allocations may be a > bigger deal there. OK. > > > Question 1: Would it be possible to increase the sample rate and track cache > > > misses as well please? > > > > If the events are constantly biased, I don't think sample rate will > > help. I don't know how the internals of profiling counters work exactly, > > but you would expect yes cache misses, and stalls from any number of > > different resources could put results in funny places. > > > > Ok, if it's stalls that are the real factor then yes, increasing the > sample rate might not help. However, the same rates for instructions > were so low, I thought it might be a combination of both low sample > count and stalls happening at particular places. A profile of cache > misses will still be useful as it'll say in general if there is a marked > increase overall or not. OK. > > Intel's OLTP workload is very sensitive to cacheline footprint of the > > kernel, and if you touch some extra cachelines at point A, it can just > > result in profile hits getting distributed all over the place. Profiling > > cache misses might help, but probably see a similar phenomenon. > > > > Interesting, this might put a hole in replacing the gfp_zone() with a > version that uses an additional (or maybe two depending on alignment) > cacheline. Well... I still think it is probably a good idea. Firstly is that it probably saves a line of icache too. Secondly, I guess adding a *single* extra readonly cacheline is probably not such a problem even for this workload. I was more thinking of if you changed the pattern in which pages are allocated (ie. like the hot/cold thing), or if some change resulted in more cross-cpu operations then it could result in worse cache efficiency. But you never know, it might be one patch to look at. > > I can't remember, does your latest patchset include any patches that change > > the possible order in which pages move around? Or is it just made up of > > straight-line performance improvement of existing implementation? > > > > It shouldn't affect order. I did a test a while ago to make sure pages > were still coming back in contiguous order as some IO cards depend on this > behaviour for performance. The intention for the first pass is a straight-line > performance improvement. OK, but the dynamic behaviour too. Free page A, free page B, allocate page A allocate page B etc. The hot/cold removal would be an obvious example of what I mean, although that wasn't included in this recent patchset anyway. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org