Messages in this thread | | | Date | Thu, 12 Mar 2020 15:56:14 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH v2] irqchip/gic-v3-its: Balance initial LPI affinity across CPUs |
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Hi John,
On 2020-03-12 15:41, John Garry wrote: > On 12/03/2020 11:55, Marc Zyngier wrote: > > Hi Marc, > >> When mapping a LPI, the ITS driver picks the first possible >> affinity, which is in most cases CPU0, assuming that if >> that's not suitable, someone will come and set the affinity >> to something more interesting. >> >> It apparently isn't the case, and people complain of poor >> performance when many interrupts are glued to the same CPU. >> So let's place the interrupts by finding the "least loaded" >> CPU (that is, the one that has the fewer LPIs mapped to it). >> So called 'managed' interrupts are an interesting case where >> the affinity is actually dictated by the kernel itself, and >> we should honor this. >> >> Reported-by: John Garry <john.garry@huawei.com> >> Link: >> https://lore.kernel.org/r/1575642904-58295-1-git-send-email-john.garry@huawei.com >> Signed-off-by: Marc Zyngier <maz@kernel.org> >> Cc: John Garry <john.garry@huawei.com> >> Cc: Ming Lei <ming.lei@redhat.com> >> --- >> Reviving this at John's request. > > Thanks very much. I may request a colleague test this due to possible > precautionary office closure.
Huh. Not great... :-(
> > The major change is that the >> affinity follows the x86 model, as described by Thomas. > > There seems to be a subtle difference between this implementation and > what Thomas described for managed interrupts handling on x86. That > being, managed interrupt loading is counted separately to total > interrupts per CPU for x86. That seems quite important so that we > spread managed interrupts evenly.
Hmmm. Yes. That'd require a separate per-CPU counter. Nothing too invasive though. I'll roll that in soon. I still wonder about interaction of collocated managed and non-managed interrupts, but we can cross that bridge later.
>> I expect this to have an impact on platforms like D05, where >> the SAS driver cannot use managed affinity just yet. > > I need some blk-mq and SCSI changes to go in first to improve the > interrupt handling there, hopefully we can make progress on that soon.
That'd be good.
Thanks,
M. -- Jazz is not dead. It just smells funny...
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