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Mon, 27 Jul 2020 22:17:58 -0400 X-MC-Unique: T0DFJtclMPSxw-AbjktqdA-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1C56A101C8A5; Tue, 28 Jul 2020 02:17:57 +0000 (UTC) Received: from T590 (ovpn-12-109.pek2.redhat.com [10.72.12.109]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ACC3890E6B; Tue, 28 Jul 2020 02:17:48 +0000 (UTC) Date: Tue, 28 Jul 2020 10:17:44 +0800 From: Ming Lei To: Jens Axboe Subject: Re: [PATCH v5 1/2] blk-mq: add tagset quiesce interface Message-ID: <20200728021744.GB1305646@T590> References: <20200727231022.307602-1-sagi@grimberg.me> <20200727231022.307602-2-sagi@grimberg.me> <20200728014038.GA1305646@T590> <1d119df0-c3af-2dfa-d569-17109733ac80@kernel.dk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <1d119df0-c3af-2dfa-d569-17109733ac80@kernel.dk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200727_221803_343505_CD4FAD81 X-CRM114-Status: GOOD ( 31.58 ) 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: Sagi Grimberg , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, Chao Leng , Keith Busch , Ming Lin , 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 07:51:16PM -0600, Jens Axboe wrote: > On 7/27/20 7:40 PM, Ming Lei wrote: > > On Mon, Jul 27, 2020 at 04:10:21PM -0700, Sagi Grimberg wrote: > >> drivers that have shared tagsets may need to quiesce potentially a lot > >> of request queues that all share a single tagset (e.g. nvme). Add an interface > >> to quiesce all the queues on a given tagset. This interface is useful because > >> it can speedup the quiesce by doing it in parallel. > >> > >> For tagsets that have BLK_MQ_F_BLOCKING set, we use call_srcu to all hctxs > >> in parallel such that all of them wait for the same rcu elapsed period with > >> a per-hctx heap allocated rcu_synchronize. for tagsets that don't have > >> BLK_MQ_F_BLOCKING set, we simply call a single synchronize_rcu as this is > >> sufficient. > >> > >> Signed-off-by: Sagi Grimberg > >> --- > >> block/blk-mq.c | 66 ++++++++++++++++++++++++++++++++++++++++++ > >> include/linux/blk-mq.h | 4 +++ > >> 2 files changed, 70 insertions(+) > >> > >> diff --git a/block/blk-mq.c b/block/blk-mq.c > >> index abcf590f6238..c37e37354330 100644 > >> --- a/block/blk-mq.c > >> +++ b/block/blk-mq.c > >> @@ -209,6 +209,42 @@ void blk_mq_quiesce_queue_nowait(struct request_queue *q) > >> } > >> EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue_nowait); > >> > >> +static void blk_mq_quiesce_blocking_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) { > >> + WARN_ON_ONCE(!(hctx->flags & BLK_MQ_F_BLOCKING)); > >> + hctx->rcu_sync = kmalloc(sizeof(*hctx->rcu_sync), GFP_KERNEL); > >> + if (!hctx->rcu_sync) > >> + continue; > > > > This approach of quiesce/unquiesce tagset is good abstraction. > > > > Just one more thing, please allocate a rcu_sync array because hctx is > > supposed to not store scratch stuff. > > I'd be all for not stuffing this in the hctx, but how would that work? > The only thing I can think of that would work reliably is batching the > queue+wait into units of N. We could potentially have many thousands of > queues, and it could get iffy (and/or unreliable) in terms of allocation > size. Looks like rcu_synchronize is 48-bytes on my local install, and it > doesn't take a lot of devices at current CPU counts to make an alloc > covering all of it huge. Let's say 64 threads, and 32 devices, then > we're already at 64*32*48 bytes which is an order 5 allocation. Not > friendly, and not going to be reliable when you need it. And if we start > batching in reasonable counts, then we're _almost_ back to doing a queue > or two at the time... 32 * 48 is 1536 bytes, so we could only do two at > the time for single page allocations. We can convert to order 0 allocation by one extra indirect array. Thanks, Ming _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme