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 C0AAAC433E0 for ; Tue, 28 Jul 2020 09:33:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A071C20714 for ; Tue, 28 Jul 2020 09:33:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="K7rbYsnk" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728129AbgG1Jdq (ORCPT ); Tue, 28 Jul 2020 05:33:46 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:46032 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728130AbgG1Jdp (ORCPT ); Tue, 28 Jul 2020 05:33:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1595928824; 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=dGU4qL4DU0btEF4z3eSCu70P6IJAwTZBKSCRVuLZFTQ=; b=K7rbYsnkaUJtEK90WxB9UhBjxbY+JwV0tvoTB0NcSOdNLFJlr8VKVBZkxTDxUe0MT9oAE0 5DTSj4/h6NodPx+SNiLEZ9YCyBC43M/C17si7XiPCvDhIFn9dxjBKV3zlJmMWVakjaOP9o R4h/YwFvvU6O4WlqMKZBhm48Xd75H8g= 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-41-WHshVYmMO3SvupRBQkriyA-1; Tue, 28 Jul 2020 05:33:42 -0400 X-MC-Unique: WHshVYmMO3SvupRBQkriyA-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 4E5EB800597; Tue, 28 Jul 2020 09:33:40 +0000 (UTC) Received: from T590 (ovpn-12-109.pek2.redhat.com [10.72.12.109]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7EB1190E63; Tue, 28 Jul 2020 09:33:31 +0000 (UTC) Date: Tue, 28 Jul 2020 17:33:26 +0800 From: Ming Lei To: Sagi Grimberg Cc: Christoph Hellwig , Jens Axboe , "Paul E. McKenney" , linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, Chao Leng , Keith Busch , Ming Lin Subject: Re: [PATCH v5 1/2] blk-mq: add tagset quiesce interface Message-ID: <20200728093326.GC1326626@T590> References: <20200727231022.307602-1-sagi@grimberg.me> <20200727231022.307602-2-sagi@grimberg.me> <20200728071859.GA21629@lst.de> <20200728091633.GB1326626@T590> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Jul 28, 2020 at 02:24:38AM -0700, Sagi Grimberg wrote: > > > > I like the tagset based interface. But the idea of doing a per-hctx > > > allocation and wait doesn't seem very scalable. > > > > > > Paul, do you have any good idea for an interface that waits on > > > multiple srcu heads? As far as I can tell we could just have a single > > > global completion and counter, and each call_srcu would just just > > > decrement it and then the final one would do the wakeup. It would just > > > be great to figure out a way to keep the struct rcu_synchronize and > > > counter on stack to avoid an allocation. > > > > > > But if we can't do with an on-stack object I'd much rather just embedd > > > the rcu_head in the hw_ctx. > > > > I think we can do that, please see the following patch which is against Sagi's V5: > > I don't think you can send a single rcu_head to multiple call_srcu calls. OK, then one variant is to put the rcu_head into blk_mq_hw_ctx, and put rcu_synchronize into blk_mq_tag_set. Thanks, Ming