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 3BC52C433E0 for ; Fri, 7 Aug 2020 13:49:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0E4B12224D for ; Fri, 7 Aug 2020 13:49:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hTE8TKGf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726256AbgHGNtu (ORCPT ); Fri, 7 Aug 2020 09:49:50 -0400 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:24421 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726282AbgHGNtt (ORCPT ); Fri, 7 Aug 2020 09:49:49 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1596808188; 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=AxKhj+gkO/EgGki1oR3mHYFMo4D2Y/mcsgmgyosbzNM=; b=hTE8TKGfJ3cCjl7RH3X0ZiWAzGpsrlq42kPTRMBy88REisEvvSpI6NO4hGsR6Z48cT4G+d N7UprgvYPHe2xp7LFJ7nBs80yC1dzXhTKy8KnUM81iMNiolppdb1ZJM61Z5J88MPCs7AWN 4N6grEIR8m68Xd3wRfAXN45Sj9oN0/0= 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-138-uNIENScWM26AP91v3UsCoQ-1; Fri, 07 Aug 2020 09:49:46 -0400 X-MC-Unique: uNIENScWM26AP91v3UsCoQ-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 8301379EEC; Fri, 7 Aug 2020 13:49:44 +0000 (UTC) Received: from T590 (ovpn-12-80.pek2.redhat.com [10.72.12.80]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 707876FEDC; Fri, 7 Aug 2020 13:49:37 +0000 (UTC) Date: Fri, 7 Aug 2020 21:49:32 +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: <20200807134932.GA2122627@T590> References: <20200807090559.29582-1-lengchao@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200807090559.29582-1-lengchao@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 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() Thanks, Ming