Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932681AbWKEMNV (ORCPT ); Sun, 5 Nov 2006 07:13:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932682AbWKEMNV (ORCPT ); Sun, 5 Nov 2006 07:13:21 -0500 Received: from brick.kernel.dk ([62.242.22.158]:5714 "EHLO kernel.dk") by vger.kernel.org with ESMTP id S932681AbWKEMNV (ORCPT ); Sun, 5 Nov 2006 07:13:21 -0500 Date: Sun, 5 Nov 2006 13:15:23 +0100 From: Jens Axboe To: Brent Baccala Cc: linux-kernel@vger.kernel.org Subject: Re: async I/O seems to be blocking on 2.6.15 Message-ID: <20061105121522.GC13555@kernel.dk> References: <20061103122055.GE13555@kernel.dk> <20061103160212.GK13555@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1677 Lines: 49 On Fri, Nov 03 2006, Brent Baccala wrote: > On Fri, 3 Nov 2006, Jens Axboe wrote: > > >Try to time it (visual output of the app is not very telling, and it's > >buffered) and then apply some profiling. > > OK, a little more info. I added gettimeofday() calls after each call > to io_submit(), put the timevals in an array, and after everything was > done computed the difference between each timeval and the program start > time, as well as the deltas. I got this: > > 0: 0.080s > 1: 0.086s 0.006s > 2: 0.102s 0.016s > 3: 0.111s 0.008s > 4: 0.118s 0.007s > 5: 0.134s 0.015s > 6: 0.141s 0.006s > 7: 0.148s 0.006s > 8: 0.158s 0.009s > 9: 0.164s 0.006s > ... > 96: 1.036s 0.007s > 97: 1.044s 0.007s > 98: 1.147s 0.102s > 99: 1.155s 0.008s > > 98 appears to be an aberration. Perhaps three of the times on an > average run are around a tenth of a second; all of the others are > pretty steady at 7 or 8 microseconds. So, it's basically linear in > its time consumption. > > Does 7 microseconds seem a bit excessive for an io_submit (and a > gettimeofday)? I guess you mean miliseconds, not microseconds. 7 miliseconds seems way too long. I repeated your test here, and the 100 submits take 97000 microseconds here - or 97 miliseconds. So that's a little less than 1 msec per io_submit. Still pretty big. You can experiment with oprofile to profile where the kernel spends its time in that period. -- Jens Axboe - 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/