From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757154AbZB0Jta (ORCPT ); Fri, 27 Feb 2009 04:49:30 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754376AbZB0JtV (ORCPT ); Fri, 27 Feb 2009 04:49:21 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:49526 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751330AbZB0JtU (ORCPT ); Fri, 27 Feb 2009 04:49:20 -0500 Subject: Re: iozone regression with 2.6.29-rc6 From: Peter Zijlstra To: Lin Ming Cc: npiggin@suse.de, linux-kernel , "Zhang, Yanmin" In-Reply-To: <1235726039.11610.243.camel@minggr> References: <1235726039.11610.243.camel@minggr> Content-Type: text/plain Date: Fri, 27 Feb 2009 10:49:14 +0100 Message-Id: <1235728154.24401.55.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.25.91 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2009-02-27 at 17:13 +0800, Lin Ming wrote: > bisect locates below commits, > > commit 1cf6e7d83bf334cc5916137862c920a97aabc018 > Author: Nick Piggin > Date: Wed Feb 18 14:48:18 2009 -0800 > > mm: task dirty accounting fix > > YAMAMOTO-san noticed that task_dirty_inc doesn't seem to be called properly for > cases where set_page_dirty is not used to dirty a page (eg. mark_buffer_dirty). > > Additionally, there is some inconsistency about when task_dirty_inc is > called. It is used for dirty balancing, however it even gets called for > __set_page_dirty_no_writeback. > > So rather than increment it in a set_page_dirty wrapper, move it down to > exactly where the dirty page accounting stats are incremented. > > Cc: YAMAMOTO Takashi > Signed-off-by: Nick Piggin > Acked-by: Peter Zijlstra > Signed-off-by: Andrew Morton > Signed-off-by: Linus Torvalds > > > below data in parenthesis is the result after above commit reverted, for example, > -10% (+2%) means, > iozone has ~10% regression with 2.6.29-rc6 compared with 2.6.29-rc5. > and > iozone has ~2% improvement with 2.6.29-rc6-revert-1cf6e7d compared with 2.6.29-rc5. > > > 4P dual-core HT 2P qual-core 2P qual-core HT > tulsa stockley Nehalem > -------------------------------------------------------- > iozone-rewrite -10% (+2%) -8% (0%) -10% (-7%) > iozone-rand-write -50% (0%) -20% (+10%) > iozone-read -13% (0%) > iozone-write -28% (-1%) > iozone-reread -5% (-1%) > iozone-mmap-read -7% (+2%) > iozone-mmap-reread -7% (+2%) > iozone-mmap-rand-read -7% (+3%) > iozone-mmap-rand-write -5% (0%) Ugh, that's unexpected.. So 'better' accounting leads to worse performance, which would indicate we throttle more. I take it you machine has gobs of memory. Does something like the below help any? --- Subject: mm: bdi: tweak task dirty penalty From: Peter Zijlstra Date: Fri Feb 27 10:41:22 CET 2009 Penalizing heavy dirtiers with 1/8-th the total dirty limit might be rather excessive on large memory machines. Use sqrt to scale it sub-linearly. Update the comment while we're there. Signed-off-by: Peter Zijlstra --- mm/page-writeback.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-) Index: linux-2.6/mm/page-writeback.c =================================================================== --- linux-2.6.orig/mm/page-writeback.c +++ linux-2.6/mm/page-writeback.c @@ -293,17 +293,21 @@ static inline void task_dirties_fraction } /* - * scale the dirty limit + * Task specific dirty limit: * - * task specific dirty limit: + * dirty -= 8 * sqrt(dirty) * p_{t} * - * dirty -= (dirty/8) * p_{t} + * Penalize tasks that dirty a lot of pages by lowering their dirty limit. This + * avoids infrequent dirtiers from getting stuck in this other guys dirty + * pages. + * + * Use a sub-linear function to scale the penalty, we only need a little room. */ static void task_dirty_limit(struct task_struct *tsk, long *pdirty) { long numerator, denominator; long dirty = *pdirty; - u64 inv = dirty >> 3; + u64 inv = 8*int_sqrt(dirty); task_dirties_fraction(tsk, &numerator, &denominator); inv *= numerator;