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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 1155DC433E0 for ; Mon, 10 Aug 2020 03:16:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D8B8D2065D for ; Mon, 10 Aug 2020 03:16:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="Nw0+ge5g" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726361AbgHJDQE (ORCPT ); Sun, 9 Aug 2020 23:16:04 -0400 Received: from us-smtp-delivery-1.mimecast.com ([207.211.31.120]:54235 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726335AbgHJDQE (ORCPT ); Sun, 9 Aug 2020 23:16:04 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1597029362; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=P2t4h3xBtgQzBZLBUDif0YVJTDr/h+7SWzN2brxDiDs=; b=Nw0+ge5g+mbc8A+r/9j6fFjBr3u9wuLk8sWjKhCH3R0vx4rkTBvzUymS1PWIaJ5tzrdiS4 QUZTAEPwiokomGgcIwd7vkiF5r9FLH1PwwDiixErYDvBl0Q/o6inxYd5lUx7SzulYX5NID HhHEVpoBSNJup8bPFDRRYiAHmJeM0FM= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-497-V_6AE8prOUqI8ObSH2fxAg-1; 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 Cc: linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, kbusch@kernel.org, axboe@fb.com, hch@lst.de, sagi@grimberg.me 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-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <61a78a78-73aa-1c67-1e8c-eae8f7c3a4e0@huawei.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.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