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([2601:647:4802:9070:4faf:1598:b15b:7e86]) by smtp.gmail.com with ESMTPSA id fa21sm201188pjb.25.2021.03.15.10.12.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Mar 2021 10:12:44 -0700 (PDT) Subject: Re: [PATCH 1/3] nvme-fabrics: only reserve a single tag To: Christoph Hellwig Cc: Keith Busch , James Smart , linux-nvme@lists.infradead.org References: <20210303125304.1200789-1-hch@lst.de> <20210303125304.1200789-2-hch@lst.de> <49d65274-002c-237b-163e-c3d482644a80@grimberg.me> <20210306070944.GA28323@lst.de> From: Sagi Grimberg Message-ID: Date: Mon, 15 Mar 2021 10:12:43 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.1 MIME-Version: 1.0 In-Reply-To: <20210306070944.GA28323@lst.de> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210315_171249_023597_37FE0C8D X-CRM114-Status: GOOD ( 16.44 ) 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: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org >>> Fabrics drivers currently reserve two tags on the admin queue. But >>> given that the connect command is only run on a freshly created queue >>> or after all commands have been force aborted we only need to reserve >>> a single tag. >> >> Umm, I think this would be an issue for non-mpath fabrics devices... >> >> When we teardown the controller, we iterate over all tags >> and cancel them, however for non-mpath devices these actually >> stick around until they exhaust the retrys counter (with the >> hope that the controller will reconnect again) unlike the mpath >> case where the requests are failed-over. >> >> Now if the admin queue is absolutely full during a reset, we won't >> have a keep-alive command. >> >> One possible solution is to make sure that >> nvme_decide_disposition to complete a request for admin >> commands. However note that this means that admin commands >> would fail immediately when the controller resets, which is >> a regression from the existing behavior and we may piss off >> users with that... > > We never retry admin commands! And the reserved tags are set aside > and not relevant to the "normal" commands. You're right, admin commands will be noretry commands. this looks good to me. Reviewed-by: Sagi Grimberg _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme