From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from brick.kernel.dk ([93.163.65.50]:53251 "EHLO kernel.dk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751377AbZGRGSU (ORCPT ); Sat, 18 Jul 2009 02:18:20 -0400 Date: Sat, 18 Jul 2009 08:18:20 +0200 From: Jens Axboe Subject: Re: fio mmap writes much slower than default writes Message-ID: <20090718061819.GF4148@kernel.dk> References: <1247751607.2689.63.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1247751607.2689.63.camel@localhost.localdomain> Sender: fio-owner@vger.kernel.org List-Id: fio@vger.kernel.org To: Richard Kennedy Cc: fio On Thu, Jul 16 2009, Richard Kennedy wrote: > Running tests of fio write with sizes that are less than the write cache > size I'm seeing a big slow down when using mmap. I'm running the tests > on linux 2.6.31-rc* x86_64. > > Typical results with default writes :- > > fio size=300m rw=write > write: io=300MiB, bw=314MiB/s, iops=80,418, runt= 955msec > > with mmap :- > > fio size=300m rw=write ioengine=mmap > write: io=300MiB, bw=55,732KiB/s, iops=13,933, runt= 5512msec > > > Is this expected or is it indicative of a problem somewhere? What does the full job file look like? Is the file cached, or are the faults reading in data? -- Jens Axboe