Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933792AbcKDAEO (ORCPT ); Thu, 3 Nov 2016 20:04:14 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:60439 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758895AbcKDAEN (ORCPT ); Thu, 3 Nov 2016 20:04:13 -0400 From: Shaohua Li To: , CC: , Subject: [PATCH V2 1/2] block: immediately dispatch big size request Date: Thu, 3 Nov 2016 17:03:53 -0700 Message-ID: <05e8cb8c7e09903c7db36e81a6bbd0b39b24deff.1478217670.git.shli@fb.com> X-Mailer: git-send-email 2.9.3 X-FB-Internal: Safe MIME-Version: 1.0 Content-Type: text/plain X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-03_06:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1862 Lines: 52 Currently block plug holds up to 16 non-mergeable requests. This makes sense if the request size is small, eg, reduce lock contention. But if request size is big enough, we don't need to worry about lock contention. Holding such request makes no sense and it lows the disk utilization. In practice, this improves 10% throughput for my raid5 sequential write workload. The size (128k) is arbitrary right now, but it makes sure lock contention is small. This probably could be more intelligent, eg, check average request size holded. Since this is mainly for sequential IO, probably not worthy. V2: check the last request instead of the first request, so as long as there is one big size request we flush the plug. Signed-off-by: Shaohua Li --- block/blk-core.c | 4 +++- include/linux/blkdev.h | 1 + 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/block/blk-core.c b/block/blk-core.c index 14d7c07..6be6378 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1763,7 +1763,9 @@ static blk_qc_t blk_queue_bio(struct request_queue *q, struct bio *bio) if (!request_count) trace_block_plug(q); else { - if (request_count >= BLK_MAX_REQUEST_COUNT) { + struct request *last = list_entry_rq(plug->list.prev); + if (request_count >= BLK_MAX_REQUEST_COUNT || + blk_rq_bytes(last) >= BLK_PLUG_FLUSH_SIZE) { blk_flush_plug_list(plug, false); trace_block_plug(q); } diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h index c47c358..72fa505 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -1078,6 +1078,7 @@ struct blk_plug { struct list_head cb_list; /* md requires an unplug callback */ }; #define BLK_MAX_REQUEST_COUNT 16 +#define BLK_PLUG_FLUSH_SIZE (128 * 1024) struct blk_plug_cb; typedef void (*blk_plug_cb_fn)(struct blk_plug_cb *, bool); -- 2.9.3