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[73.241.217.19]) by smtp.gmail.com with ESMTPSA id u68sm2663115pfu.219.2021.02.09.07.24.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 09 Feb 2021 07:24:15 -0800 (PST) Subject: Re: [PATCH V2 0/2] nvme: Support for fused NVME_IOCTL_SUBMIT_IO To: Keith Busch , Clay Mayers References: <20210105224939.1336-2-clay.mayers@kioxia.com> <20210125195844.1390581-1-clay.mayers@kioxia.com> <20210209031252.GA97526@C02WT3WMHTD6> From: Bart Van Assche Message-ID: Date: Tue, 9 Feb 2021 07:24:12 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: <20210209031252.GA97526@C02WT3WMHTD6> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210209_102419_663663_42AA73E8 X-CRM114-Status: GOOD ( 22.25 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jens Axboe , "linux-nvme@lists.infradead.org" , Sagi Grimberg , Chaitanya Kulkarni , Christoph Hellwig 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 On 2/8/21 7:12 PM, Keith Busch wrote: > On Tue, Feb 09, 2021 at 12:53:17AM +0000, Clay Mayers wrote: >> Is there any other feedback on V2? >> >> My main concern I have about my implementation is how fused requests >> are tunneled through the mq request layer. The 1st request is marked as >> started but it won't be in the device until the 2nd command is queued. As >> Keith pointed out, a device reset can split the two so care must be taken to >> correctly handle this case. Despite this, I thought this was a better approach >> than modifying mq requests to be fused. Especially given Christoph's >> concern of cost vs value. This is the lightest touch I could come up with. >> >> Further consideration of this patch may need a more compelling use case. >> I've worked on a proprietary storage systems that relied on fused NVMeOF >> support so it seems compelling to me. There's a comment in target/core.c >> that there is "no support for fused commands yet" implying it's been >> considered. Is pci only support for fused too soon or too little? What would >> make it more compelling? > > The complications it introduces to the IO path and error handling for an > archaic feature has me on the "Nak" side. NVMeOF was introduced well after the > spec define Reservations, and the kernel has supported that capability for many > years. I'm not aware of any other use case for fused commands, so it appears to > be dead weight in the spec. Hi Keith, Do you agree that NVMe persistent reservation commands apply to an NVMe namespace in its entirety while fused compare-and-write commands allow to implement locking for subsets of the LBA range of a namespace? In other words, I think there is a valid use case for fused commands. Thanks, Bart. _______________________________________________ Linux-nvme mailing list Linux-nvme@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-nvme