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Mon, 27 Jul 2020 22:28:15 -0400 X-MC-Unique: cWzPJ-mtMWWxGoe2LqL3_w-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 45DC1100CCC0; Tue, 28 Jul 2020 02:28:14 +0000 (UTC) Received: from T590 (ovpn-12-109.pek2.redhat.com [10.72.12.109]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E942C71D06; Tue, 28 Jul 2020 02:28:06 +0000 (UTC) Date: Tue, 28 Jul 2020 10:28:02 +0800 From: Ming Lei To: Jens Axboe Subject: Re: [PATCH v5 1/2] blk-mq: add tagset quiesce interface Message-ID: <20200728022802.GC1305646@T590> References: <20200727231022.307602-1-sagi@grimberg.me> <20200727231022.307602-2-sagi@grimberg.me> <20200728014038.GA1305646@T590> <1d119df0-c3af-2dfa-d569-17109733ac80@kernel.dk> <20200728021744.GB1305646@T590> <5fce2096-2ed2-b396-76a7-5fb8ea97a389@kernel.dk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <5fce2096-2ed2-b396-76a7-5fb8ea97a389@kernel.dk> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200727_222818_744108_381D6C30 X-CRM114-Status: GOOD ( 32.20 ) 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 08:23:15PM -0600, Jens Axboe wrote: > On 7/27/20 8:17 PM, Ming Lei wrote: > > 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. > > I guess that could work, and would just be one extra alloc + free if we > still retain the batch. That'd take it to 16 devices (at 32 CPUs) per > round, potentially way less of course if we have more CPUs. So still > somewhat limiting, rather than do all at once. With the approach in blk_mq_alloc_rqs(), each allocated page can be added to one list, so the indirect array can be saved. Then it is possible to allocate for any size queues/devices since every allocation is just for single page in case that it is needed, even no pre-calculation is required. Thanks, Ming _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme