From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:36958 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757258Ab3BSHrh (ORCPT ); Tue, 19 Feb 2013 02:47:37 -0500 Date: Tue, 19 Feb 2013 08:46:09 +0100 From: Jens Axboe Subject: Re: Timing information between I/Os in iolog replay Message-ID: <20130219074608.GC26519@kernel.dk> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: fio-owner@vger.kernel.org List-Id: fio@vger.kernel.org To: Alireza Haghdoost Cc: fio@vger.kernel.org On Tue, Feb 19 2013, Alireza Haghdoost wrote: > Hi, > > I am trying to understand how fio respect timing information between > consecutive IOs in a read_iolog job, However the logic is not very > clear for me , specially in the following function: > > static int read_iolog2(struct thread_data *td, FILE *f) > { > ... > r = sscanf(p, "%256s %256s %llu %u", fname, act, &offset, > &bytes); > ... > if (!strcmp(act, "wait")) > rw = DDIR_WAIT; > ... > if (rw == DDIR_WAIT) { > ipo->delay = offset; > ... > queue_io_piece(td, ipo); > } > > Here is my two questions about this function: > First, I can not see any "wait" command in a typical iolog file > (collected with write_iolog=str job option). Should I set special > parameter in job file to collect iolog with respect to IO timing > information. > Second, Why request offset assigned to ipo->delay ? I was thinking > that ipo->delay should get some timing value which represent > inter-submission time delay. However, In this case ipo->delay get LBA > offset which just a byte address in my point view. That is the format of a delay line, instead of an LBA it has a timing parameter. Normally you don't have delays at all, it's only for replay and record of blktraces that would be a factor. -- Jens Axboe