Messages in this thread | | | Subject | Re: Question on handling managed IRQs when hotplugging CPUs | From | John Garry <> | Date | Wed, 30 Jan 2019 10:38:18 +0000 |
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On 29/01/2019 17:20, Keith Busch wrote: > 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.
I wouldn't say that this behaviour is obvious to the developer. I can't see anything in Documentation/PCI/MSI-HOWTO.txt
It also seems that this policy to rely on upper layer to flush+freeze queues would cause issues if managed IRQs are used by drivers in other subsystems. Networks controllers may have multiple queues and unsoliciated interrupts.
Thanks, John
> > . >
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