Re: blk-mq: improvement CPU hotplug (simplified version) v3

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On 2020-05-21 19:39, Ming Lei wrote:
> You may argue that two hw queue may share single managed interrupt, that
> is possible if driver plays the trick. But if driver plays the trick in
> this way, it is driver's responsibility to guarantee that the managed
> irq won't be shutdown if either of the two hctxs are active, such as,
> making sure that hctx->cpumask + hctx->cpumask <= this managed interrupt's affinity.
> It is definitely one strange enough case, and this patch doesn't
> suppose to cover this strange case. But, this patch won't break this
> case. Also just be curious, do you have such in-tree case? and are you
> sure the driver uses managed interrupt?

I'm concerned about the block drivers that use RDMA (NVMeOF, SRP, iSER,
...). The functions that accept an interrupt vector argument
(comp_vector), namely ib_alloc_cq() and ib_create_cq(), can be used in
such a way that completion interrupts are handled on another CPU than
those in hctx->cpumask.

Bart.



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