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Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [LSF/MM/BPF BOF] Userspace command abouts To: Keith Busch , Chaitanya Kulkarni Cc: Sagi Grimberg , "hch@lst.de" , "martin.petersen@oracle.com" , "dgilbert@interlog.com" , Hannes Reinecke , "linux-nvme@lists.infradead.org" , "linux-block@vger.kernel.org" , "linux-scsi@vger.kernel.org" , "lsf-pc@lists.linuxfoundation.org" References: <3d3369f1-7ebe-b3b8-804c-ff2b97ec679d@suse.de> <57d8dff9-2fdb-8198-6cdc-7265797a704a@interlog.com> <23526cf9-d912-59a7-4742-6003d6ccfd45@grimberg.me> <561afa67-04d0-c675-6bbb-048313da152b@grimberg.me> <73b4dd39-9ce8-9b55-8a1d-06865f3bde32@nvidia.com> Content-Language: en-US From: Damien Le Moal Organization: Western Digital Research In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 2/25/23 10:51, Keith Busch wrote: > On Fri, Feb 24, 2023 at 11:54:39PM +0000, Chaitanya Kulkarni wrote: >> I do think that we should work on CDL for NVMe as it will solve some of >> the timeout related problems effectively than using aborts or any other >> mechanism. > > That proposal exists in NVMe TWG, but doesn't appear to have recent activity. > The last I heard, one point of contention was where the duration limit property > exists: within the command, or the queue. From my perspective, if it's not at > the queue level, the limit becomes meaningless, but hey, it's not up to me. Limit attached to the command makes things more flexible and easier for the host, so personally, I prefer that. But this has an impact on the controller: the device needs to pull in *all* commands to be able to know the limits and do scheduling/aborts appropriately. That is not something that the device designers like, for obvious reasons (device internal resources...). On the other hand, limits attached to queues could lead to either a serious increase in the number of queues (PCI space & number of IRQ vectors limits), or, loss of performance as a particular queue with the desired limit would be accessed from multiple CPUs on the host (lock contention). Tricky problem I think with lots of compromises. -- Damien Le Moal Western Digital Research