From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1D18FC43441 for ; Thu, 29 Nov 2018 02:51:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DD44E2081C for ; Thu, 29 Nov 2018 02:51:53 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DD44E2081C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-block-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727411AbeK2Nzk (ORCPT ); Thu, 29 Nov 2018 08:55:40 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58366 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727022AbeK2Nzk (ORCPT ); Thu, 29 Nov 2018 08:55:40 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D7EDFA6DE0; Thu, 29 Nov 2018 02:51:52 +0000 (UTC) Received: from ming.t460p (ovpn-8-23.pek2.redhat.com [10.72.8.23]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 5838B6A6A2; Thu, 29 Nov 2018 02:51:47 +0000 (UTC) Date: Thu, 29 Nov 2018 10:51:44 +0800 From: Ming Lei To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-nvme@lists.infradead.org Subject: Re: [PATCH 5/8] virtio_blk: implement mq_ops->commit_rqs() hook Message-ID: <20181129025143.GC23390@ming.t460p> References: <20181126163556.5181-1-axboe@kernel.dk> <20181126163556.5181-6-axboe@kernel.dk> <20181128021029.GF11128@ming.t460p> <35b33a34-9e24-5acb-7a4e-57433328bf3d@kernel.dk> <20181129012342.GB23249@ming.t460p> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.1 (2017-09-22) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Thu, 29 Nov 2018 02:51:52 +0000 (UTC) Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Wed, Nov 28, 2018 at 07:19:09PM -0700, Jens Axboe wrote: > On 11/28/18 6:23 PM, Ming Lei wrote: > > On Tue, Nov 27, 2018 at 07:34:51PM -0700, Jens Axboe wrote: > >> On 11/27/18 7:10 PM, Ming Lei wrote: > >>> On Mon, Nov 26, 2018 at 09:35:53AM -0700, Jens Axboe wrote: > >>>> We need this for blk-mq to kick things into gear, if we told it that > >>>> we had more IO coming, but then failed to deliver on that promise. > >>>> > >>>> Signed-off-by: Jens Axboe > >>>> --- > >>>> drivers/block/virtio_blk.c | 15 +++++++++++++++ > >>>> 1 file changed, 15 insertions(+) > >>>> > >>>> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c > >>>> index 6e869d05f91e..b49c57e77780 100644 > >>>> --- a/drivers/block/virtio_blk.c > >>>> +++ b/drivers/block/virtio_blk.c > >>>> @@ -214,6 +214,20 @@ static void virtblk_done(struct virtqueue *vq) > >>>> spin_unlock_irqrestore(&vblk->vqs[qid].lock, flags); > >>>> } > >>>> > >>>> +static void virtio_commit_rqs(struct blk_mq_hw_ctx *hctx) > >>>> +{ > >>>> + struct virtio_blk *vblk = hctx->queue->queuedata; > >>>> + int qid = hctx->queue_num; > >>>> + bool kick; > >>>> + > >>>> + spin_lock_irq(&vblk->vqs[qid].lock); > >>>> + kick = virtqueue_kick_prepare(vblk->vqs[qid].vq); > >>>> + spin_unlock_irq(&vblk->vqs[qid].lock); > >>>> + > >>>> + if (kick) > >>>> + virtqueue_notify(vblk->vqs[qid].vq); > >>>> +} > >>>> + > >>>> static blk_status_t virtio_queue_rq(struct blk_mq_hw_ctx *hctx, > >>>> const struct blk_mq_queue_data *bd) > >>>> { > >>>> @@ -638,6 +652,7 @@ static void virtblk_initialize_rq(struct request *req) > >>>> > >>>> static const struct blk_mq_ops virtio_mq_ops = { > >>>> .queue_rq = virtio_queue_rq, > >>>> + .commit_rqs = virtio_commit_rqs, > >>>> .complete = virtblk_request_done, > >>>> .init_request = virtblk_init_request, > >>>> #ifdef CONFIG_VIRTIO_BLK_SCSI > >>>> -- > >>>> 2.17.1 > >>>> > >>> > >>> If .commit_rqs() is implemented, virtqueue_notify() in virtio_queue_rq() > >>> should have been removed for saving the world switch per .queue_rq() > >> > >> ->commits_rqs() is only for the case where bd->last is set to false, > >> and we never make it to the end and flag bd->last == true. If bd->last > >> is true, the driver should kick things into gear. > > > > OK, looks I misunderstood it. However, virtio-blk doesn't need this > > change since virtio_queue_rq() can handle it well. This patch may introduce > > one unnecessary VM world switch in case of queue busy. > > Not it won't, it may in the case of some failure outside of the driver. If the failure is because of out of tag, blk_mq_dispatch_wake() will rerun the queue, and the bd->last will be set finally. Or is there other failure(outside of driver) not covered? > The only reason that virtio-blk doesn't currently hang is because it > has restart logic, and the failure case only happens in the if we > already have IO in-flight. Yeah, virtqueue_kick() is called in case of any error in virtio_queue_rq(), so I am still wondering why we have to implement .commit_rqs() for virtio-blk. > For the NVMe variant, that's not going to be the case. OK. > > > IMO bd->last won't work well in case of io scheduler given the rq_list > > only includes one single request. > > But that's a fake limitation that definitely should just be lifted, > the fact that blk-mq-sched is _currently_ just doing single requests > is woefully inefficient. I agree, but seems a bit hard given we have to consider request merge. > > > I wrote this kind of patch(never posted) before to use sort of > > ->commits_rqs() to replace the current bd->last mechanism which need > > one extra driver tag, which may improve the above case, also code gets > > cleaned up. > > It doesn't need one extra driver tag, we currently get an extra one just > to flag ->last correctly. That's not a requirement, that's a limitation > of the current implementation. We could get rid of that, and it it > proves to be an issue, that's not hard to do. What do you think about using .commit_rqs() to replace ->last? For example, just call .commit_rqs() after the last request is queued to driver successfully. Then we can remove bd->last and avoid to get the extra tag for figuring out bd->last. Thanks, Ming