On Tue, Jan 29, 2019 at 05:12:40PM +0000, John Garry wrote: > On 29/01/2019 15:44, Keith Busch wrote: > > > > Hm, we used to freeze the queues with CPUHP_BLK_MQ_PREPARE callback, > > which would reap all outstanding commands before the CPU and IRQ are > > taken offline. That was removed with commit 4b855ad37194f ("blk-mq: > > Create hctx for each present CPU"). It sounds like we should bring > > something like that back, but make more fine grain to the per-cpu context. > > > > Seems reasonable. But we would need it to deal with drivers where they only > expose a single queue to BLK MQ, but use many queues internally. I think > megaraid sas does this, for example. > > I would also be slightly concerned with commands being issued from the > driver unknown to blk mq, like SCSI TMF.
I don't think either of those descriptions sound like good candidates for using managed IRQ affinities.