Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751086AbbB1HaZ (ORCPT ); Sat, 28 Feb 2015 02:30:25 -0500 Received: from mga14.intel.com ([192.55.52.115]:7173 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750766AbbB1HaY (ORCPT ); Sat, 28 Feb 2015 02:30:24 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.09,666,1418112000"; d="scan'208";a="684740794" Message-ID: <1425108604.10337.84.camel@linux.intel.com> Subject: Re: [LKP] [mm] 3484b2de949: -46.2% aim7.jobs-per-min From: Huang Ying To: Mel Gorman Cc: LKML , LKP ML Date: Sat, 28 Feb 2015 15:30:04 +0800 In-Reply-To: <20150228014642.GG3087@suse.de> References: <1425021696.10337.55.camel@linux.intel.com> <20150228014642.GG3087@suse.de> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.9-1+b1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2094 Lines: 53 On Sat, 2015-02-28 at 01:46 +0000, Mel Gorman wrote: > On Fri, Feb 27, 2015 at 03:21:36PM +0800, Huang Ying wrote: > > FYI, we noticed the below changes on > > > > git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master > > commit 3484b2de9499df23c4604a513b36f96326ae81ad ("mm: rearrange zone fields into read-only, page alloc, statistics and page reclaim lines") > > > > The perf cpu-cycles for spinlock (zone->lock) increased a lot. I suspect there are some cache ping-pong or false sharing. > > > > Are you sure about this result? I ran similar tests here and found that > there was a major regression introduced near there but it was commit > 05b843012335 ("mm: memcontrol: use root_mem_cgroup res_counter") that > cause the problem and it was later reverted. On local tests on a 4-node > machine, commit 3484b2de9499df23c4604a513b36f96326ae81ad was within 1% > of the previous commit and well within the noise. After applying the below debug patch, the performance regression restored. So I think we can root cause this regression to be cache line alignment related issue? If my understanding were correct, after the 3484b2de94, lock and low address area free_area are in the same cache line, so that the cache line of the lock and the low address area of free_area will be switched between MESI "E" and "S" state because it is written in one CPU (page allocating with free_area) and frequently read (spinning on lock) in another CPU. Best Regards, Huang, Ying --- include/linux/mmzone.h | 2 ++ 1 file changed, 2 insertions(+) --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -468,6 +468,8 @@ struct zone { /* Write-intensive fields used from the page allocator */ spinlock_t lock; + ZONE_PADDING(_pad_xx_) + /* free areas of different sizes */ struct free_area free_area[MAX_ORDER]; -- 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/