Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754274AbYGYOyU (ORCPT ); Fri, 25 Jul 2008 10:54:20 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751708AbYGYOyL (ORCPT ); Fri, 25 Jul 2008 10:54:11 -0400 Received: from gw.goop.org ([64.81.55.164]:55833 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751732AbYGYOyK (ORCPT ); Fri, 25 Jul 2008 10:54:10 -0400 Message-ID: <4889E90D.2000807@goop.org> Date: Fri, 25 Jul 2008 07:54:05 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.14 (X11/20080501) MIME-Version: 1.0 To: Alex Nixon CC: Nick Piggin , "Alex Nixon (Intern)" , Andi Kleen , Peter Zijlstra , Ingo Molnar , Linux Kernel Mailing List , Ian Campbell , "Theodore Ts'o" , Alexander Viro , Andrew Morton Subject: Re: Large increase in context switch rate References: <487E43D9.7080703@goop.org> <87mykgrxtv.fsf@basil.nowhere.org> <0E902970173AF84089673FA54B7FE78A329073@lonpexch01.citrite.net> <200807241126.48364.nickpiggin@yahoo.com.au> <4889B9AE.3050108@citrix.com> In-Reply-To: <4889B9AE.3050108@citrix.com> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2029 Lines: 57 Alex Nixon wrote: > The relevant changeset had caused the blocksize to default to 1024 (as opposed > to 4096) - as a result there was a large increase in the time spent waiting on > pipes. > Good work! > Instead of re-adding the line taken out of fs/pipe.c by Theodore I opted instead > to change the default block size for pseudo-filesystems to PAGE_SIZE, to try > avoid making pipe.c inconsistent with Theodore's new approach. > > The performance penalty from these extra context switches is fairly small, but > is magnified when virtualization is involved, hence the desire to keep it lower > if possible. > > > From 4b568a72fc42b52279507eb4d1339e0637ae719a Mon Sep 17 00:00:00 2001 > From: Alex Nixon > Date: Fri, 25 Jul 2008 11:26:44 +0100 > Subject: [PATCH] VFS: increase pseudo-filesystem block size to PAGE_SIZE. > > Changeset ba52de123d454b57369f291348266d86f4b35070 caused the block size used > by pseudo-filesystems to decrease from PAGE_SIZE to 1024 leading to a doubling > of the number of context switches during a kernbench run. > Probably worth explicitly noting the effect on pipe buffer size. > Signed-off-by: Alex Nixon > --- > fs/libfs.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/libfs.c b/fs/libfs.c > index baeb71e..1add676 100644 > --- a/fs/libfs.c > +++ b/fs/libfs.c > @@ -216,8 +216,8 @@ int get_sb_pseudo(struct file_system_type *fs_type, char *name, > > s->s_flags = MS_NOUSER; > s->s_maxbytes = ~0ULL; > - s->s_blocksize = 1024; > - s->s_blocksize_bits = 10; > + s->s_blocksize = PAGE_SIZE; > + s->s_blocksize_bits = PAGE_SHIFT; > s->s_magic = magic; > s->s_op = ops ? ops : &simple_super_operations; > s->s_time_gran = 1; > J -- 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/