Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753468AbbKLN0G (ORCPT ); Thu, 12 Nov 2015 08:26:06 -0500 Received: from mx2.suse.de ([195.135.220.15]:34288 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753290AbbKLN0B (ORCPT ); Thu, 12 Nov 2015 08:26:01 -0500 From: Jan Kara To: Jens Axboe Cc: Jeff Moyer , LKML , Jan Kara Subject: [PATCH] blk-flush: Queue through IO scheduler when flush not required Date: Thu, 12 Nov 2015 14:25:52 +0100 Message-Id: <1447334752-31027-1-git-send-email-jack@suse.com> X-Mailer: git-send-email 2.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1678 Lines: 42 Currently blk_insert_flush() just adds flush request to q->queue_head when flush is not required. That completely bypasses IO scheduler so e.g. CFQ can be idling waiting for new request to arrive and will idle through the whole window unnecessarily. Luckily this only happens in rare cases as usually checks in generic_make_request_checks() clear FLUSH and FUA flags early if they are not needed. When no flushing is actually required, we can easily fix the problem by properly queueing the request through the IO scheduler. Ideally IO scheduler should be also made aware of requests queued via blk_flush_queue_rq(). However inserting flush request through IO scheduler can have unwanted side-effects since due to flush batching delaying the flush request in IO scheduler will delay all flush requests possibly coming from other processes. So we keep adding the request directly to q->queue_head. Signed-off-by: Jan Kara --- block/blk-flush.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/block/blk-flush.c b/block/blk-flush.c index 9c423e53324a..c81d56ec308f 100644 --- a/block/blk-flush.c +++ b/block/blk-flush.c @@ -422,7 +422,7 @@ void blk_insert_flush(struct request *rq) if (q->mq_ops) { blk_mq_insert_request(rq, false, false, true); } else - list_add_tail(&rq->queuelist, &q->queue_head); + q->elevator->type->ops.elevator_add_req_fn(q, rq); return; } -- 2.1.4 -- 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/