From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752793AbWLSGix (ORCPT ); Tue, 19 Dec 2006 01:38:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752789AbWLSGix (ORCPT ); Tue, 19 Dec 2006 01:38:53 -0500 Received: from smtp108.mail.mud.yahoo.com ([209.191.85.218]:33257 "HELO smtp108.mail.mud.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752724AbWLSGiw (ORCPT ); Tue, 19 Dec 2006 01:38:52 -0500 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:X-YMail-OSG:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type; b=ydBozdbnEj3tAdHUgeBt57nCcpVIrT7btevJ1MMCgWi0l0tGwK7PnrkeaDR3/lfK1mwVfw6xSGYWbtY0aucqIlybBzmYI+mTuOTUFOmm4RA2HdlkVTz0IY03GxkNEe8+d/YeAI4zELxr8heHP0AWsg6fFkIBBGEt6mkQ127CzFs= ; X-YMail-OSG: r9aozTgVM1mYx2QrcXmOjDgpdAQeapBywVh2G7hjIvA0Jf0fVAh0HtfIsxrQfSxYSXc5LkxMQIbpZ53zsCFUL0E8EvqSHD7e1GwfZl7L8AOKQ37Mt6kn8RbjE0azuSxyqYkEfY8mvJoRD4Q- Message-ID: <458788D7.2070107@yahoo.com.au> Date: Tue, 19 Dec 2006 17:38:15 +1100 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.12) Gecko/20051007 Debian/1.7.12-1 X-Accept-Language: en MIME-Version: 1.0 To: Manish Regmi CC: Erik Mouw , kernelnewbies@nl.linux.org, linux-kernel@vger.kernel.org Subject: Re: Linux disk performance. References: <652016d30612172007m58d7a828q378863121ebdc535@mail.gmail.com> <1166431020.3365.931.camel@laptopd505.fenrus.org> <652016d30612180439y6cd12089l115e4ef6ce2e59fe@mail.gmail.com> <20061218130702.GA14984@gateway.home> <652016d30612182222h7fde4ea5jbc0927c8ebeae76a@mail.gmail.com> In-Reply-To: <652016d30612182222h7fde4ea5jbc0927c8ebeae76a@mail.gmail.com> Content-Type: multipart/mixed; boundary="------------040407040209040306090302" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org This is a multi-part message in MIME format. --------------040407040209040306090302 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Manish Regmi wrote: > Nick Piggin: > >> but >> they look like they might be a (HZ quantised) delay coming from >> block layer plugging. > > > Sorry i didnīt understand what you mean. When you submit a request to an empty block device queue, it can get "plugged" for a number of timer ticks before any IO is actually started. This is done for efficiency reasons and is independent of the IO scheduler used. Use the noop IO scheduler, as well as the attached patch, and let's see what your numbers look like. Thanks, Nick -- SUSE Labs, Novell Inc. --------------040407040209040306090302 Content-Type: text/plain; name="block-no-plug.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="block-no-plug.patch" Index: linux-2.6/block/ll_rw_blk.c =================================================================== --- linux-2.6.orig/block/ll_rw_blk.c 2006-12-19 17:35:00.000000000 +1100 +++ linux-2.6/block/ll_rw_blk.c 2006-12-19 17:35:53.000000000 +1100 @@ -226,6 +226,8 @@ void blk_queue_make_request(request_queu q->unplug_delay = (3 * HZ) / 1000; /* 3 milliseconds */ if (q->unplug_delay == 0) q->unplug_delay = 1; + q->unplug_delay = 0; + q->unplug_thresh = 0; INIT_WORK(&q->unplug_work, blk_unplug_work, q); --------------040407040209040306090302-- Send instant messages to your online friends http://au.messenger.yahoo.com