Messages in this thread | | | Subject | Re: [PATCH RFC 1/1] genirq: Make threaded handler use irq affinity for managed interrupt | Date | Mon, 23 Dec 2019 09:07:39 +0000 | From | Marc Zyngier <> |
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On 2019-12-20 23:31, Ming Lei wrote: > On Fri, Dec 20, 2019 at 03:38:24PM +0000, John Garry wrote: >> > > 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@kernel.org/T/#t >> > > >> > > >> > > >> https://lore.kernel.org/linux-block/20191218071942.22336-1-ming.lei@redhat.com/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. > > Lots of CPU lockup can is performance issue if there isn't obvious > bug. > > I am wondering if you may explain it a bit why enabling SMMU may save > CPU a it?
The other way around. mapping/unmapping IOVAs doesn't comes for free. I'm trying to find out whether the NVMe map/unmap patterns trigger something unexpected in the SMMU driver, but that's a very long shot.
M. -- Jazz is not dead. It just smells funny...
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