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[46.117.125.14]) by smtp.gmail.com with ESMTPSA id l6-20020adfa386000000b0020c6a524fd5sm6744909wrb.99.2022.05.21.13.03.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 21 May 2022 13:03:05 -0700 (PDT) Message-ID: <85a65656-5b1f-d2d8-b075-11bccadc8508@grimberg.me> Date: Sat, 21 May 2022 23:03:04 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.8.1 Subject: Re: [PATCH 0/3] nvme-tcp: queue stalls under high load Content-Language: en-US To: Hannes Reinecke , Christoph Hellwig Cc: Keith Busch , linux-nvme@lists.infradead.org References: <20220519062617.39715-1-hare@suse.de> <64f57dcf-f3d2-d1db-782e-4f48c542754d@grimberg.me> <23ab4753-593f-e44a-b768-0c1d3682abb0@suse.de> From: Sagi Grimberg In-Reply-To: <23ab4753-593f-e44a-b768-0c1d3682abb0@suse.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220521_130308_073260_4C9A681A X-CRM114-Status: GOOD ( 12.93 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org >>> Hi all, >>> >>> one of our partners registered queue stalls and I/O timeouts under >>> high load. Analysis revealed that we see an extremely 'choppy' I/O >>> behaviour when running large transfers on systems on low-performance >>> links (eg 1GigE networks). >>> We had a system with 30 queues trying to transfer 128M requests; simple >>> calculation shows that transferring a _single_ request on all queues >>> will take up to 38 seconds, thereby timing out the last request before >>> it got sent. >>> As a solution I first fixed up the timeout handler to reset the timeout >>> if the request is still queued or in the process of being send. The >>> second path modifies the send path to only allow for new requests if we >>> have enough space on the TX queue, and finally break up the send loop to >>> avoid system stalls when sending large request. >> >> What is the average latency you are seeing with this test? >> I'm guessing more than 30 seconds :) > > Yes, of course. Simple maths, in the end. > (Actually it's more as we're always triggering a reconnect cycle...) > And telling the customer to change his testcase only helps _so_ much. Not to change the test case, simply making the io_timeout substantially larger.