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=-6.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 D3662C433E3 for ; Tue, 28 Jul 2020 07:48:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A7F1522B3F for ; Tue, 28 Jul 2020 07:48:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727833AbgG1Hsm (ORCPT ); Tue, 28 Jul 2020 03:48:42 -0400 Received: from mail-pj1-f66.google.com ([209.85.216.66]:38169 "EHLO mail-pj1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727815AbgG1Hsl (ORCPT ); Tue, 28 Jul 2020 03:48:41 -0400 Received: by mail-pj1-f66.google.com with SMTP id e22so3900556pjt.3 for ; Tue, 28 Jul 2020 00:48:41 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=FO3oZnFQw3BE/aK5FD2/kGmXgS1zOp4LbjFEtdo3Kss=; b=LntcwYwUsYSUNNlTEWGBGBVHAIIYqMXjpRfx6Pbvso1hT7HJFsE5o/LKoDeqshCac5 MIO64+GlmlkdMnSLQku/ntVmLQ8GxU9nfEjcEKIp59BpGECioPQ3RUuDV8EqgEuixStD /x9QqDiUMDaATPQaSiNhfwh7XsEsgRBsK1HO2j241Da/Dg3a5qUiXohTIp687Bqblj35 qlXd0UTSDrjrtH1jGeNAt/1EHKymoA21bnfGnMwf3uuHrjKqHP4D+2MUHjwzH4TNLIm/ cWyDTG2CTmPbo4Hq0CatKXEJr58WtIR6y8qQe3217XBxX20mLsYVVKUVXgYckow1eB/S VW8g== X-Gm-Message-State: AOAM531F+y8rrh0wMcJOqof3JsUMgCh7TFL466HOLYPDdmLtr+hserF7 dcZSSQHBYZJzzfPwFDTpeYg= X-Google-Smtp-Source: ABdhPJxiF2YrVEmDeu79GtOv5OlVjYPIrvmpdEyZkbJPAMTCqudVVziGKdUAmW3UYNHmAKI5+Eva1Q== X-Received: by 2002:a17:90b:1249:: with SMTP id gx9mr3200688pjb.149.1595922521144; Tue, 28 Jul 2020 00:48:41 -0700 (PDT) Received: from ?IPv6:2601:647:4802:9070:541c:8b1b:5ac:35fe? ([2601:647:4802:9070:541c:8b1b:5ac:35fe]) by smtp.gmail.com with ESMTPSA id s23sm2000848pjs.47.2020.07.28.00.48.39 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 28 Jul 2020 00:48:40 -0700 (PDT) Subject: Re: [PATCH v5 1/2] blk-mq: add tagset quiesce interface To: Christoph Hellwig Cc: linux-nvme@lists.infradead.org, Keith Busch , Jens Axboe , linux-block@vger.kernel.org, Ming Lin , Chao Leng , "Paul E. McKenney" References: <20200727231022.307602-1-sagi@grimberg.me> <20200727231022.307602-2-sagi@grimberg.me> <20200728071859.GA21629@lst.de> From: Sagi Grimberg Message-ID: <54c7f095-c112-eaa7-3c69-65b4b48f2688@grimberg.me> Date: Tue, 28 Jul 2020 00:48:39 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200728071859.GA21629@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org > I like the tagset based interface. Even that we need to unquiesce back the connect_q? See my comment on v5. Kinda bothers me... But the idea of doing a per-hctx > allocation and wait doesn't seem very scalable. I belong to this camp too.. > 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.