From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:56868 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730571AbeIXS0p (ORCPT ); Mon, 24 Sep 2018 14:26:45 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Laurence Oberman , Omar Sandoval , Bart Van Assche , Kashyap Desai , Christoph Hellwig , Ming Lei , Jens Axboe , Sasha Levin Subject: [PATCH 4.14 154/173] blk-mq: only attempt to merge bio if there is rq in sw queue Date: Mon, 24 Sep 2018 13:53:08 +0200 Message-Id: <20180924113126.619573489@linuxfoundation.org> In-Reply-To: <20180924113114.334025954@linuxfoundation.org> References: <20180924113114.334025954@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: 4.14-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ming Lei [ Upstream commit b04f50ab8a74129b3041a2836c33c916be3c6667 ] Only attempt to merge bio iff the ctx->rq_list isn't empty, because: 1) for high-performance SSD, most of times dispatch may succeed, then there may be nothing left in ctx->rq_list, so don't try to merge over sw queue if it is empty, then we can save one acquiring of ctx->lock 2) we can't expect good merge performance on per-cpu sw queue, and missing one merge on sw queue won't be a big deal since tasks can be scheduled from one CPU to another. Cc: Laurence Oberman Cc: Omar Sandoval Cc: Bart Van Assche Tested-by: Kashyap Desai Reported-by: Kashyap Desai Reviewed-by: Christoph Hellwig Signed-off-by: Ming Lei Signed-off-by: Jens Axboe Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- block/blk-mq-sched.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/block/blk-mq-sched.c +++ b/block/blk-mq-sched.c @@ -236,7 +236,8 @@ bool __blk_mq_sched_bio_merge(struct req return e->type->ops.mq.bio_merge(hctx, bio); } - if (hctx->flags & BLK_MQ_F_SHOULD_MERGE) { + if ((hctx->flags & BLK_MQ_F_SHOULD_MERGE) && + !list_empty_careful(&ctx->rq_list)) { /* default per sw-queue merge */ spin_lock(&ctx->lock); ret = blk_mq_attempt_merge(q, ctx, bio);