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Mon, 27 Jul 2020 21:09:41 -0400 X-MC-Unique: EODb3-lnNu2XjM7cLv6kGA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id CF983800468; Tue, 28 Jul 2020 01:09:39 +0000 (UTC) Received: from T590 (ovpn-12-109.pek2.redhat.com [10.72.12.109]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 898F810013D0; Tue, 28 Jul 2020 01:09:32 +0000 (UTC) Date: Tue, 28 Jul 2020 09:09:28 +0800 From: Ming Lei To: Sagi Grimberg Subject: Re: [PATCH v3 1/2] blk-mq: add async quiesce interface Message-ID: <20200728010928.GA1303645@T590> References: <20200726002301.145627-1-sagi@grimberg.me> <20200726002301.145627-2-sagi@grimberg.me> <20200726093132.GD1110104@T590> <9ac5f658-31b3-bb19-e5fe-385a629a7d67@grimberg.me> <20200727020803.GC1129253@T590> <2c2ae567-6953-5b7f-2fa1-a65e287b5a9d@grimberg.me> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200727_210944_074288_53469D8F X-CRM114-Status: GOOD ( 33.26 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jens Axboe , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, Chao Leng , Keith Busch , Christoph Hellwig Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Mon, Jul 27, 2020 at 02:00:15PM -0700, Sagi Grimberg wrote: > > > > > > > > +void blk_mq_quiesce_queue_async(struct request_queue *q) > > > > > > > +{ > > > > > > > + struct blk_mq_hw_ctx *hctx; > > > > > > > + unsigned int i; > > > > > > > + > > > > > > > + blk_mq_quiesce_queue_nowait(q); > > > > > > > + > > > > > > > + queue_for_each_hw_ctx(q, hctx, i) { > > > > > > > + init_completion(&hctx->rcu_sync.completion); > > > > > > > + init_rcu_head(&hctx->rcu_sync.head); > > > > > > > + if (hctx->flags & BLK_MQ_F_BLOCKING) > > > > > > > + call_srcu(hctx->srcu, &hctx->rcu_sync.head, > > > > > > > + wakeme_after_rcu); > > > > > > > + else > > > > > > > + call_rcu(&hctx->rcu_sync.head, > > > > > > > + wakeme_after_rcu); > > > > > > > + } > > > > > > > > > > > > Looks not necessary to do anything in case of !BLK_MQ_F_BLOCKING, and single > > > > > > synchronize_rcu() is OK for all hctx during waiting. > > > > > > > > > > That's true, but I want a single interface for both. v2 had exactly > > > > > that, but I decided that this approach is better. > > > > > > > > Not sure one new interface is needed, and one simple way is to: > > > > > > > > 1) call blk_mq_quiesce_queue_nowait() for each request queue > > > > > > > > 2) wait in driver specific way > > > > > > > > Or just wondering why nvme doesn't use set->tag_list to retrieve NS, > > > > then you may add per-tagset APIs for the waiting. > > > > > > Because it puts assumptions on how quiesce works, which is something > > > I'd like to avoid because I think its cleaner, what do others think? > > > Jens? Christoph? > > > > I'd prefer to have it in a helper, and just have blk_mq_quiesce_queue() > > call that. > > I agree with this approach as well. > > Jens, this mean that we use the call_rcu mechanism also for non-blocking > hctxs, because the caller will call it for multiple request queues (see > patch 2) and we don't want to call synchronize_rcu for every request > queue serially, we want it to happen in parallel. > > Which leaves us with the patchset as it is, just to convert the > rcu_synchronize structure to be dynamically allocated on the heap > rather than keeping it statically allocated in the hctx. > > This is how it looks: > -- > diff --git a/block/blk-mq.c b/block/blk-mq.c > index abcf590f6238..d913924117d2 100644 > --- a/block/blk-mq.c > +++ b/block/blk-mq.c > @@ -209,6 +209,52 @@ void blk_mq_quiesce_queue_nowait(struct request_queue > *q) > } > EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait); > > +void blk_mq_quiesce_queue_async(struct request_queue *q) > +{ > + struct blk_mq_hw_ctx *hctx; > + unsigned int i; > + int rcu = false; > + > + blk_mq_quiesce_queue_nowait(q); > + > + queue_for_each_hw_ctx(q, hctx, i) { > + hctx->rcu_sync = kmalloc(sizeof(*hctx->rcu_sync), > GFP_KERNEL); > + if (!hctx->rcu_sync) { > + /* fallback to serial rcu sync */ > + if (hctx->flags & BLK_MQ_F_BLOCKING) > + synchronize_srcu(hctx->srcu); > + else > + rcu = true; > + } else { > + init_completion(&hctx->rcu_sync->completion); > + init_rcu_head(&hctx->rcu_sync->head); > + if (hctx->flags & BLK_MQ_F_BLOCKING) > + call_srcu(hctx->srcu, &hctx->rcu_sync->head, > + wakeme_after_rcu); > + else > + call_rcu(&hctx->rcu_sync->head, > + wakeme_after_rcu); > + } > + } > + if (rcu) > + synchronize_rcu(); > +} > +EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_async); > + > +void blk_mq_quiesce_queue_async_wait(struct request_queue *q) > +{ > + struct blk_mq_hw_ctx *hctx; > + unsigned int i; > + > + queue_for_each_hw_ctx(q, hctx, i) { > + if (!hctx->rcu_sync) > + continue; > + wait_for_completion(&hctx->rcu_sync->completion); > + destroy_rcu_head(&hctx->rcu_sync->head); > + } > +} > +EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_async_wait); > + > /** > * blk_mq_quiesce_queue() - wait until all ongoing dispatches have finished > * @q: request queue. > diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h > index 23230c1d031e..7213ce56bb31 100644 > --- a/include/linux/blk-mq.h > +++ b/include/linux/blk-mq.h > @@ -5,6 +5,7 @@ > #include > #include > #include > +#include > > struct blk_mq_tags; > struct blk_flush_queue; > @@ -170,6 +171,7 @@ struct blk_mq_hw_ctx { > */ > struct list_head hctx_list; > > + struct rcu_synchronize *rcu_sync; The above pointer needn't to be added to blk_mq_hw_ctx, and it can be allocated on heap and passed to the waiting helper. Thanks, Ming _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme