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Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH 0/3] nvme-tcp: queue stalls under high load Content-Language: en-US To: Sagi Grimberg , Christoph Hellwig Cc: Keith Busch , linux-nvme@lists.infradead.org References: <20220519062617.39715-1-hare@suse.de> <64f57dcf-f3d2-d1db-782e-4f48c542754d@grimberg.me> From: Hannes Reinecke In-Reply-To: <64f57dcf-f3d2-d1db-782e-4f48c542754d@grimberg.me> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220520_110152_269425_DDE17FBE X-CRM114-Status: GOOD ( 14.73 ) 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 On 5/20/22 11:20, Sagi Grimberg wrote: > >> 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. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), GF: Felix Imendörffer