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Sun, 09 Aug 2020 23:16:00 -0400 X-MC-Unique: V_6AE8prOUqI8ObSH2fxAg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6AA2380183C; Mon, 10 Aug 2020 03:15:59 +0000 (UTC) Received: from T590 (ovpn-13-99.pek2.redhat.com [10.72.13.99]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D43048BA11; Mon, 10 Aug 2020 03:15:51 +0000 (UTC) Date: Mon, 10 Aug 2020 11:15:47 +0800 From: Ming Lei To: Chao Leng Subject: Re: [PATCH v2 0/3] reduce quiesce time for lots of name spaces Message-ID: <20200810031547.GB2202641@T590> References: <20200807090559.29582-1-lengchao@huawei.com> <20200807134932.GA2122627@T590> <61a78a78-73aa-1c67-1e8c-eae8f7c3a4e0@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <61a78a78-73aa-1c67-1e8c-eae8f7c3a4e0@huawei.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200809_231606_141444_84395CAD X-CRM114-Status: GOOD ( 20.74 ) 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: axboe@fb.com, sagi@grimberg.me, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, kbusch@kernel.org, hch@lst.de 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, Aug 10, 2020 at 10:17:04AM +0800, Chao Leng wrote: > > > On 2020/8/7 21:49, Ming Lei wrote: > > On Fri, Aug 07, 2020 at 05:05:59PM +0800, Chao Leng wrote: > > > nvme_stop_queues quiesce queues for all name spaces, now quiesce one by > > > one, if there is lots of name spaces, sync wait long time(more than 10s). > > > Multipath can not fail over to retry quickly, cause io pause long time. > > > This is not expected. > > > To reduce quiesce time, we introduce async mechanism for sync SRCUs > > > and quiesce queue. > > > > > > > Frankly speaking, I prefer to replace SRCU with percpu_refcount: > > > > - percpu_refcount has much less memory footprint than SRCU, so we can simply > > move percpu_refcount into request_queue, instead of adding more bytes > > into each hctx by this patch > > > > - percpu_ref_get()/percpu_ref_put() isn't slower than srcu_read_lock()/srcu_read_unlock(). > > > > - with percpu_refcount, we can remove 'srcu_idx' from hctx_lock/hctx_unlock() > IO pause long time if fail over, this is a serios problem. we need fix > it as soon as possible. SRCU is just used for blocking queue, The issue has been long time since SRCU is taken, not sure if it is something urgent. > non blocking queue need 0 bytes. So more bytes(just 24 bytes) is not > waste. > > About using per_cpu to replace SRCU, I suggest separate discussion. > Can you show the patch? This will make it easier to discuss. https://lore.kernel.org/linux-block/20200728134938.1505467-1-ming.lei@redhat.com/ Thanks, Ming _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme