Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity for managed interrupt

[John Garry]

> > We've got some more results and it looks promising.
> >
> > So with your patch we get a performance boost of 3180.1K -> 3294.9K
> > IOPS in the D06 SAS env. Then when we change the driver to use
> > threaded interrupt handler (mainline currently uses tasklet), we get a
> > boost again up to 3415K IOPS.
> >
> > Now this is essentially the same figure we had with using threaded
> > handler + the gen irq change in spreading the handler CPU affinity. We
> > did also test your patch + gen irq change and got a performance drop,
> > to 3347K IOPS.
> >
> > So tentatively I'd say your patch may be all we need.
>
> OK.
>
> > FYI, here is how the effective affinity is looking for both SAS
> > controllers with your patch:
> >
> > 74:02.0
> > irq 81, cpu list 24-29, effective list 24 cq
> > irq 82, cpu list 30-35, effective list 30 cq
>
> Cool.
>
> [...]
>
> > As for your patch itself, I'm still concerned of possible regressions
> > if we don't apply this effective interrupt affinity spread policy to
> > only managed interrupts.
>
> I'll try and revise that as I post the patch, probably at some point
> between now and Christmas. I still think we should find a way to
> address this for the D05 SAS driver though, maybe by managing the
> affinity yourself in the driver. But this requires experimentation.

I've already done something experimental for the driver to manage the 
affinity, and performance is generally much better:

https://github.com/hisilicon/kernel-dev/commit/e15bd404ed1086fed44da34ed3bd37a8433688a7

But I still think it's wise to only consider managed interrupts for now.

> > JFYI, about NVMe CPU lockup issue, there are 2 works on going here:
> >
> > https://lore.kernel.org/linux-nvme/20191209175622.1964-1-kbusch@xxxxxxxxxx/T/#t 
> >
> >
> > https://lore.kernel.org/linux-block/20191218071942.22336-1-ming.lei@xxxxxxxxxx/T/#t 
>
> I've also managed to trigger some of them now that I have access to
> a decent box with nvme storage. 

I only have 2x NVMe SSDs when this occurs - I should not be hitting this...

Out of curiosity, have you tried
> with the SMMU disabled? I'm wondering whether we hit some livelock
> condition on unmapping buffers...

No, but I can give it a try. Doing that should lower the CPU usage, 
though, so maybe masks the issue - probably not.

Much appreciated,
John