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([2601:647:4000:d7:89ed:1db3:8c60:ba90]) by smtp.gmail.com with ESMTPSA id y2sm2896316pfq.16.2020.05.08.16.39.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 08 May 2020 16:39:48 -0700 (PDT) Subject: Re: [PATCH V10 07/11] blk-mq: stop to handle IO and drain IO before hctx becomes inactive To: Ming Lei , Jens Axboe Cc: linux-block@vger.kernel.org, John Garry , Hannes Reinecke , Christoph Hellwig , Thomas Gleixner References: <20200505020930.1146281-1-ming.lei@redhat.com> <20200505020930.1146281-8-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: Fri, 8 May 2020 16:39:46 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200505020930.1146281-8-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 2020-05-04 19:09, Ming Lei wrote: > -static bool blk_mq_get_driver_tag(struct request *rq) > +static bool blk_mq_get_driver_tag(struct request *rq, bool direct_issue) > { > if (rq->tag != -1) > return true; > - return __blk_mq_get_driver_tag(rq); > + > + if (!__blk_mq_get_driver_tag(rq)) > + return false; > + /* > + * In case that direct issue IO process is migrated to other CPU > + * which may not belong to this hctx, add one memory barrier so we > + * can order driver tag assignment and checking BLK_MQ_S_INACTIVE. > + * Otherwise, barrier() is enough given both setting BLK_MQ_S_INACTIVE > + * and driver tag assignment are run on the same CPU because > + * BLK_MQ_S_INACTIVE is only set after the last CPU of this hctx is > + * becoming offline. > + * > + * Process migration might happen after the check on current processor > + * id, smp_mb() is implied by processor migration, so no need to worry > + * about it. > + */ > + if (unlikely(direct_issue && rq->mq_ctx->cpu != raw_smp_processor_id())) > + smp_mb(); > + else > + barrier(); > + > + if (unlikely(test_bit(BLK_MQ_S_INACTIVE, &rq->mq_hctx->state))) { > + blk_mq_put_driver_tag(rq); > + return false; > + } > + return true; > } How much does this patch slow down the hot path? Can CPU migration be fixed without affecting the hot path, e.g. by using the request queue freezing mechanism? Thanks, Bart.