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
