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Tue, 24 May 2022 08:08:51 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 8EhFBZOSjGLeWwAAMHmgww (envelope-from ); Tue, 24 May 2022 08:08:51 +0000 Message-ID: <76475e4f-13c7-2e0c-8584-f46918f5cefa@suse.de> Date: Tue, 24 May 2022 10:08:50 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.4.0 Subject: Re: [PATCH 1/3] nvme-tcp: spurious I/O timeout 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> <20220519062617.39715-2-hare@suse.de> <7827d599-7714-3947-ee24-e343e90eee6e@grimberg.me> <96a3315f-43a4-efe6-1f37-0552d66dbd85@suse.de> <96722b37-f943-c3e4-ee6a-440f65e8afca@grimberg.me> <7ec792e3-5110-2272-b6fe-1a976c8c054f@grimberg.me> <919bfaa2-a35d-052a-1d35-9fdd8faa0d3f@suse.de> <02805f44-6f2d-b12e-c224-d44616332d5a@grimberg.me> From: Hannes Reinecke In-Reply-To: <02805f44-6f2d-b12e-c224-d44616332d5a@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-20220524_010852_717481_810C7C21 X-CRM114-Status: GOOD ( 31.43 ) 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 5/24/22 09:57, Sagi Grimberg wrote: > >>>>>> I'm open to discussion what we should be doing when the request is >>>>>> in the process of being sent. But when it didn't have a chance to >>>>>> be sent and we just overloaded our internal queuing we shouldn't >>>>>> be sending timeouts. >>>>> >>>>> As mentioned above, what happens if that same reporter opens >>>>> another bug >>>>> that the same phenomenon happens with soft-iwarp? What would you tell >>>>> him/her? >>>> >>>> Nope. It's a HW appliance. Not a chance to change that. >>> >>> It was just a theoretical question. >>> >>> Do note that I'm not against solving a problem for anyone, I'm just >>> questioning if increasing the io_timeout to be unbound in case the >>> network is congested, is the right solution for everyone instead of >>> a particular case that can easily be solved with udev to make the >>> io_timeout to be as high as needed. >>> >>> One can argue that this patchset is making nvme-tcp to basically >>> ignore the device io_timeout in certain cases. >> >> Oh, yes, sure, that will happen. >> What I'm actually arguing is the imprecise difference between >> BLK_STS_AGAIN / BLK_STS_RESOURCE as a return value from ->queue_rq() >> and command timeouts in case of resource constraints on the driver >> implementing ->queue_rq(). >> >> If there is a resource constrain driver is free to return >> BLK_STS_RESOURCE (in which case you wouldn't see a timeout) or accept >> the request (in which case there will be a timeout). > > There is no resource constraint. The driver sizes up the resources > to be able to queue all the requests it is getting. > >> I could live with a timeout if that would just result in the command >> being retried. But in the case of nvme it results in a connection >> reset to boot, making customers really nervous that their system is >> broken. > > But how does the driver know that it is running in this environment that > is completely congested? What I'm saying is that this is a specific use > case that the solution can have negative side-effects for other common > use-cases, because it is beyond the scope of the driver to handle. > > We can also trigger this condition with nvme-rdma. > > We could stay with this patch, but I'd argue that this might be the > wrong thing to do in certain use-cases. > Right, okay. Arguably this is a workload corner case, and we might not want to fix this in the driver. _However_: do we need to do a controller reset in this case? Shouldn't it be sufficient to just complete the command w/ timeout error and be done with it? Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), Geschäftsführer: Ivo Totev, Andrew Myers, Andrew McDonald, Martje Boudien Moerman