From mboxrd@z Thu Jan 1 00:00:00 1970 From: Theodore Ts'o Subject: Re: ext4_fallocate Date: Thu, 28 Jun 2012 08:48:34 -0400 Message-ID: <20120628124834.GA5313@thunk.org> References: <4FE8086F.4070506@zoho.com> <20120625085159.GA18931@gmail.com> <20120625191744.GB9688@thunk.org> <4FE9B57F.4030704@redhat.com> <4FE9F9F4.7010804@zoho.com> <4FEA0DD1.8080403@gmail.com> <4FEA1415.8040809@redhat.com> <4FEA1F18.6010206@redhat.com> <20120627193034.GA3198@thunk.org> <4FEB9115.6090309@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ric Wheeler , Fredrick , Ric Wheeler , linux-ext4@vger.kernel.org, Andreas Dilger , wenqing.lz@taobao.com To: Eric Sandeen Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:53262 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751299Ab2F1Msp (ORCPT ); Thu, 28 Jun 2012 08:48:45 -0400 Content-Disposition: inline In-Reply-To: <4FEB9115.6090309@redhat.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, Jun 27, 2012 at 07:02:45PM -0400, Eric Sandeen wrote: > > fallocate 1g, do 16m of 4k random IOs, sync after each: > > # for I in a b c; do rm -f testfile; echo 3 > /proc/sys/vm/drop_caches; fio tytso.fio | grep 2>&1 WRITE; done > > WRITE: io=16384KB, aggrb=154KB/s, minb=158KB/s, maxb=158KB/s, mint=105989msec, maxt=105989msec > WRITE: io=16384KB, aggrb=163KB/s, minb=167KB/s, maxb=167KB/s, mint=99906msec, maxt=99906msec > WRITE: io=16384KB, aggrb=176KB/s, minb=180KB/s, maxb=180KB/s, mint=92791msec, maxt=92791msec > > same, but overwrite pre-written 1g file (same as the expose-my-data option ;) > > # dd if=/dev/zero of=testfile bs=1M count=1024 > # for I in a b c; do echo 3 > /proc/sys/vm/drop_caches; fio tytso.fio | grep 2>&1 WRITE; done > > WRITE: io=16384KB, aggrb=164KB/s, minb=168KB/s, maxb=168KB/s, mint=99515msec, maxt=99515msec > WRITE: io=16384KB, aggrb=164KB/s, minb=168KB/s, maxb=168KB/s, mint=99371msec, maxt=99371msec > WRITE: io=16384KB, aggrb=164KB/s, minb=168KB/s, maxb=168KB/s, mint=99677msec, maxt=99677msec > There's a pretty large range comparing the first set versus the second set of numbers. With the second set of numbers, the times are much more stable. I wonder if one of the things that's going on is file placement; if you're constantly deleting and recreating the file, are we getting the same block numbers or not? (And if we're not, is that something we need to look at vis-a-vis the block allocator --- especially with SSD's?) - Ted