Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262413AbVDLNTi (ORCPT ); Tue, 12 Apr 2005 09:19:38 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262353AbVDLNEy (ORCPT ); Tue, 12 Apr 2005 09:04:54 -0400 Received: from smtp208.mail.sc5.yahoo.com ([216.136.130.116]:19897 "HELO smtp208.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S262413AbVDLMtx (ORCPT ); Tue, 12 Apr 2005 08:49:53 -0400 Message-ID: <425BC3ED.9050202@yahoo.com.au> Date: Tue, 12 Apr 2005 22:49:49 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.6) Gecko/20050324 Debian/1.7.6-1 X-Accept-Language: en MIME-Version: 1.0 To: Andrew Morton CC: Jens Axboe , linux-kernel , "Chen, Kenneth W" Subject: [patch 4/9] blk: no memory barrier References: <425BC262.1070500@yahoo.com.au> In-Reply-To: <425BC262.1070500@yahoo.com.au> Content-Type: multipart/mixed; boundary="------------050604070906030108020808" Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1848 Lines: 53 This is a multi-part message in MIME format. --------------050604070906030108020808 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit 4/9 -- SUSE Labs, Novell Inc. --------------050604070906030108020808 Content-Type: text/plain; name="blk-no-mb.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="blk-no-mb.patch" This memory barrier is not needed because the waitqueue will only get waiters on it in the following situations: rq->count has exceeded the threshold - however all manipulations of ->count are performed under the runqueue lock, and so we will correctly pick up any waiter. Memory allocation for the request fails. In this case, there is no additional help provided by the memory barrier. We are guaranteed to eventually wake up waiters because the request allocation mempool guarantees that if the mem allocation for a request fails, there must be some requests in flight. They will wake up waiters when they are retired. Signed-off-by: Nick Piggin Index: linux-2.6/drivers/block/ll_rw_blk.c =================================================================== --- linux-2.6.orig/drivers/block/ll_rw_blk.c 2005-04-12 22:05:44.000000000 +1000 +++ linux-2.6/drivers/block/ll_rw_blk.c 2005-04-12 22:26:13.000000000 +1000 @@ -1828,7 +1828,6 @@ static void __freed_request(request_queu clear_queue_congested(q, rw); if (rl->count[rw] + 1 <= q->nr_requests) { - smp_mb(); if (waitqueue_active(&rl->wait[rw])) wake_up(&rl->wait[rw]); --------------050604070906030108020808-- - 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/