Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S264690AbTFLCiZ (ORCPT ); Wed, 11 Jun 2003 22:38:25 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264696AbTFLCiY (ORCPT ); Wed, 11 Jun 2003 22:38:24 -0400 Received: from dyn-ctb-210-9-241-68.webone.com.au ([210.9.241.68]:37380 "EHLO chimp.local.net") by vger.kernel.org with ESMTP id S264690AbTFLCiQ (ORCPT ); Wed, 11 Jun 2003 22:38:16 -0400 Message-ID: <3EE7EAB2.5010705@cyberone.com.au> Date: Thu, 12 Jun 2003 12:51:30 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.3) Gecko/20030327 Debian/1.3-4 X-Accept-Language: en MIME-Version: 1.0 To: Nick Piggin CC: Andrea Arcangeli , Chris Mason , Marc-Christian Petersen , Jens Axboe , Marcelo Tosatti , Georg Nikodym , lkml , Matthias Mueller Subject: Re: [PATCH] io stalls References: <1055296630.23697.195.camel@tiny.suse.com> <20030611021030.GQ26270@dualathlon.random> <1055353360.23697.235.camel@tiny.suse.com> <20030611181217.GX26270@dualathlon.random> <1055356032.24111.240.camel@tiny.suse.com> <20030611183503.GY26270@dualathlon.random> <3EE7D1AA.30701@cyberone.com.au> <20030612012951.GG1500@dualathlon.random> <1055384547.24111.322.camel@tiny.suse.com> <3EE7E876.80808@cyberone.com.au> <20030612024608.GE1415@dualathlon.random> <3EE7EA4A.5030105@cyberone.com.au> In-Reply-To: <3EE7EA4A.5030105@cyberone.com.au> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2387 Lines: 73 Nick Piggin wrote: > > > Andrea Arcangeli wrote: > >> On Thu, Jun 12, 2003 at 12:41:58PM +1000, Nick Piggin wrote: >> >>> >>> Chris Mason wrote: >>> >>> >>>> On Wed, 2003-06-11 at 21:29, Andrea Arcangeli wrote: >>>> >>>> >>>> >>>>> this will avoid get_request_wait_wakeup to mess the wakeup, so we can >>>>> wakep_nr(rq.count) safely. >>>>> >>>>> then there's the last issue raised by Chris, that is if we get >>>>> request >>>>> released faster than the tasks can run, still we can generate a not >>>>> perfect fairness. My solution to that is to change wake_up to have a >>>>> nr_exclusive not obeying to the try_to_wakeup retval. that should >>>>> guarantee exact FIFO then, but it's a minor issue because the >>>>> requests >>>>> shouldn't be released systematically in a flood. So I'm leaving it >>>>> opened for now, the others already addressed should be the major >>>>> ones. >>>>> >>>>> >>>> I think the only time we really need to wakeup more than one waiter is >>>> when we hit the q->batch_request mark. After that, each new request >>>> that is freed can be matched with a single waiter, and we know that >>>> any >>>> previously finished requests have probably already been matched to >>>> their >>>> own waiter. >>>> >>>> >>>> >>> Nope. Not even then. Each retiring request should submit >>> a wake up, and the process will submit another request. >>> So the number of requests will be held at the batch_request >>> mark until no more waiters. >>> >>> Now that begs the question, why have batch_requests anymore? >>> It no longer does anything. >>> >> >> it does nothing w/ _exclusive and w/o the wake_up_nr, that's why I added >> the wake_up_nr. >> >> > That is pretty pointless as well. You might as well just start > waking up at the queue full limit, and wake one at a time. > > The purpose for batch_requests was I think for devices with a > very small request size, to reduce context switches. I guess you could fix this by having a "last woken" flag, and allow that process to allocate requests without blocking from the batch limit until the queue full limit. That is how batch_requests is supposed to work. - 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/