Messages in this thread | | | Date | Thu, 06 May 2021 12:44:21 +0100 | From | Marc Zyngier <> | Subject | Re: [PATCH v3 03/16] arm64: Allow IPIs to be handled as normal interrupts |
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On Thu, 06 May 2021 08:50:42 +0100, He Ying <heying24@huawei.com> wrote: > > Hello Marc, > > We have faced a performance regression for handling ipis since this > commit. I think it's the same issue reported by Vincent.
Can you share more details on what regression you have observed? What's the workload, the system, the performance drop?
> I found you pointed out the possible two causes: > > (1) irq_enter/exit on the rescheduling IPI means we reschedule much > more often.
It turned out to be a red herring. We don't reschedule more often, but we instead suffer from the overhead of irq_enter()/irq_exit(). However, this only matters for silly benchmarks, and no real-life workload showed any significant regression. Have you identified such realistic workload?
> (2) irq_domain lookups add some overhead.
While this is also a potential source of overhead, it turned out not to be the case.
> But I don't see any following patches in mainline. So, are you still > working on this issue? Looking forward to your reply.
See [1]. However, there is probably better things to do than this low-level specialisation of IPIs, and Thomas outlined what needs to be done (see v1 of the patch series).
Thanks,
M.
[1] https://lore.kernel.org/lkml/20201124141449.572446-1-maz@kernel.org/
-- Without deviation from the norm, progress is not possible.
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