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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 3CAC3C433DF for ; Fri, 15 May 2020 03:55:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1EF552065F for ; Fri, 15 May 2020 03:55:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727910AbgEODzj (ORCPT ); Thu, 14 May 2020 23:55:39 -0400 Received: from mail-pl1-f176.google.com ([209.85.214.176]:34933 "EHLO mail-pl1-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726665AbgEODzj (ORCPT ); Thu, 14 May 2020 23:55:39 -0400 Received: by mail-pl1-f176.google.com with SMTP id q16so409253plr.2 for ; Thu, 14 May 2020 20:55:37 -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:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=vb1WtJaUpKjPUeuSdPV1jFSQUyMjEpEylrC8Q1F61Uo=; b=fglVlO1HuRYOnrfZk/LJlHnma1mjWERClhAsOoL5ooLBxAMLXARQCBs1ttwpIoPItv NwliCvbK3qv0tpLRlBHeIqC81YAZKtxmoCBBB+j7SIAh8Y1Zddla+K1KjPb8HrSUKLdO JRZ8y4Qk5yXK3bPpaFh0zdkNyStiCxerpZ1qYCDonvjmmVioGCUQR9bor2Ujer2EH0l5 GXxaHj7TfqS/faCslGPJRkGBaodzqHG6AryyT806LpfBKEKoMqCIpCfHyhaGAapi7Qq9 lTMCUft1lfp+1ssfIcGD/8JOWA9I+k6zahKlplFp4vAwlHbtt7GQ/4LCTR6phxYpR9U0 kk7A== X-Gm-Message-State: AOAM530Y+kOrpbkGca3LWZFh4FOSsEW2+RqUMS9/RQu5wnj2t/5GvOuC o0LL+oWJ+h79AN2ke8MtGxSY+ZMj X-Google-Smtp-Source: ABdhPJxp/tIeHmN36sSyJ90da3FHtoIqWzS73jygdXgp2VbPQcOHEZ/elZkZEKPwEIH4J8EAWEjqIQ== X-Received: by 2002:a17:902:8c8f:: with SMTP id t15mr1720387plo.183.1589514936450; Thu, 14 May 2020 20:55:36 -0700 (PDT) Received: from ?IPv6:2601:647:4000:d7:3d24:1780:a4ad:9b1e? ([2601:647:4000:d7:3d24:1780:a4ad:9b1e]) by smtp.gmail.com with ESMTPSA id q7sm553688pgs.13.2020.05.14.20.55.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 14 May 2020 20:55:35 -0700 (PDT) Subject: Re: [PATCH 6/6] blk-mq: stop to allocate new requst and drain request before hctx becomes inactive To: Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, John Garry , Hannes Reinecke , Christoph Hellwig , Thomas Gleixner References: <20200515014153.2403464-1-ming.lei@redhat.com> <20200515014153.2403464-7-ming.lei@redhat.com> From: Bart Van Assche Autocrypt: addr=bvanassche@acm.org; prefer-encrypt=mutual; keydata= mQENBFSOu4oBCADcRWxVUvkkvRmmwTwIjIJvZOu6wNm+dz5AF4z0FHW2KNZL3oheO3P8UZWr LQOrCfRcK8e/sIs2Y2D3Lg/SL7qqbMehGEYcJptu6mKkywBfoYbtBkVoJ/jQsi2H0vBiiCOy fmxMHIPcYxaJdXxrOG2UO4B60Y/BzE6OrPDT44w4cZA9DH5xialliWU447Bts8TJNa3lZKS1 AvW1ZklbvJfAJJAwzDih35LxU2fcWbmhPa7EO2DCv/LM1B10GBB/oQB5kvlq4aA2PSIWkqz4 3SI5kCPSsygD6wKnbRsvNn2mIACva6VHdm62A7xel5dJRfpQjXj2snd1F/YNoNc66UUTABEB AAG0JEJhcnQgVmFuIEFzc2NoZSA8YnZhbmFzc2NoZUBhY20ub3JnPokBOQQTAQIAIwUCVI67 igIbAwcLCQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEHFcPTXFzhAJ8QkH/1AdXblKL65M Y1Zk1bYKnkAb4a98LxCPm/pJBilvci6boefwlBDZ2NZuuYWYgyrehMB5H+q+Kq4P0IBbTqTa jTPAANn62A6jwJ0FnCn6YaM9TZQjM1F7LoDX3v+oAkaoXuq0dQ4hnxQNu792bi6QyVdZUvKc macVFVgfK9n04mL7RzjO3f+X4midKt/s+G+IPr4DGlrq+WH27eDbpUR3aYRk8EgbgGKvQFdD CEBFJi+5ZKOArmJVBSk21RHDpqyz6Vit3rjep7c1SN8s7NhVi9cjkKmMDM7KYhXkWc10lKx2 RTkFI30rkDm4U+JpdAd2+tP3tjGf9AyGGinpzE2XY1K5AQ0EVI67igEIAKiSyd0nECrgz+H5 PcFDGYQpGDMTl8MOPCKw/F3diXPuj2eql4xSbAdbUCJzk2ETif5s3twT2ER8cUTEVOaCEUY3 eOiaFgQ+nGLx4BXqqGewikPJCe+UBjFnH1m2/IFn4T9jPZkV8xlkKmDUqMK5EV9n3eQLkn5g lco+FepTtmbkSCCjd91EfThVbNYpVQ5ZjdBCXN66CKyJDMJ85HVr5rmXG/nqriTh6cv1l1Js T7AFvvPjUPknS6d+BETMhTkbGzoyS+sywEsQAgA+BMCxBH4LvUmHYhpS+W6CiZ3ZMxjO8Hgc ++w1mLeRUvda3i4/U8wDT3SWuHcB3DWlcppECLkAEQEAAYkBHwQYAQIACQUCVI67igIbDAAK CRBxXD01xc4QCZ4dB/0QrnEasxjM0PGeXK5hcZMT9Eo998alUfn5XU0RQDYdwp6/kMEXMdmT oH0F0xB3SQ8WVSXA9rrc4EBvZruWQ+5/zjVrhhfUAx12CzL4oQ9Ro2k45daYaonKTANYG22y //x8dLe2Fv1By4SKGhmzwH87uXxbTJAUxiWIi1np0z3/RDnoVyfmfbbL1DY7zf2hYXLLzsJR mSsED/1nlJ9Oq5fALdNEPgDyPUerqHxcmIub+pF0AzJoYHK5punqpqfGmqPbjxrJLPJfHVKy goMj5DlBMoYqEgpbwdUYkH6QdizJJCur4icy8GUNbisFYABeoJ91pnD4IGei3MTdvINSZI5e Message-ID: Date: Thu, 14 May 2020 20:55:34 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200515014153.2403464-7-ming.lei@redhat.com> Content-Type: text/plain; charset=utf-8 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 On 2020-05-14 18:41, Ming Lei wrote: > + /* Prevent new request from being allocated on the current hctx/cpu */ > + set_bit(BLK_MQ_S_INACTIVE, &hctx->state); What guarantees that this change has been observed by all CPUs before the blk_mq_tags_has_request() loop finishes? > + /* > + * Grab one refcount for avoiding scheduler switch, and > + * return immediately if queue has been frozen. > + */ > + if (!percpu_ref_tryget(&q->q_usage_counter)) > + return 0; If percpu_ref_tryget(&q->q_usage_counter) fails that means either that request queue freezing is in progress or that a request queue has been frozen. I don't think that it is safe to return immediately if request queue freezing is still in progress. > + /* wait until all requests in this hctx are gone */ > + while (blk_mq_tags_has_request(hctx)) > + msleep(5); > + > + percpu_ref_put(&q->q_usage_counter); > + return 0; > +} Thanks, Bart.