From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756552Ab2DFR1E (ORCPT ); Fri, 6 Apr 2012 13:27:04 -0400 Received: from mail-pb0-f46.google.com ([209.85.160.46]:49964 "EHLO mail-pb0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752624Ab2DFR1C (ORCPT ); Fri, 6 Apr 2012 13:27:02 -0400 Message-ID: <4F7F2765.3090003@kernel.org> Date: Fri, 06 Apr 2012 11:27:01 -0600 From: Shaohua Li User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:11.0) Gecko/20120327 Thunderbird/11.0.1 MIME-Version: 1.0 To: "linux-kernel@vger.kernel.org" CC: "axboe@kernel.dk" Subject: [PATCH]block: make auto block plug flush threshold per-disk based Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Subject: block: make auto block plug flush threshold per-disk based We do auto block plug flush to reduce latency, the threshold is 16 requests. This works well if the task is accessing one or two drives. The problem is if the task is accessing a raid 0 device and the raid disk number is big, say 8 or 16, 16/8 = 2 or 16/16=1, we will have heavy lock contention. This patch makes the threshold per-disk based. The latency should be still ok accessing one or two drives. The setup with application accessing a lot of drives in the meantime uaually is big machine, avoiding lock contention is more important, because any contention will actually increase latency. Signed-off-by: Shaohua Li --- block/blk-core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) Index: linux/block/blk-core.c =================================================================== --- linux.orig/block/blk-core.c 2012-04-06 10:51:29.766932123 -0600 +++ linux/block/blk-core.c 2012-04-06 10:56:46.386929357 -0600 @@ -1277,7 +1277,8 @@ list_for_each_entry_reverse(rq, &plug->list, queuelist) { int el_ret; - (*request_count)++; + if (rq->q == q) + (*request_count)++; if (rq->q != q || !blk_rq_merge_ok(rq, bio)) continue;