Messages in this thread | | | Subject | Re: [PATCH v3 03/16] arm64: Allow IPIs to be handled as normal interrupts | From | He Ying <> | Date | Fri, 7 May 2021 15:30:06 +0800 |
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在 2021/5/6 19:44, Marc Zyngier 写道: > 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?
OK. We have just calculated the pmu cycles from the entry of gic_handle_irq
to the entry of do_handle_ipi. Here is some more information about our test:
CPU: Hisilicon hip05-d02
Applying the patch series: 1115 cycles
Reverting the patch series: 599 cycles
> >> 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?
I'm afraid not. We just run some benchmarks and calculated pmu cycle counters.
But we have observed running time from the entry of gic_handle_irq to the entry
of do_handle_ipi almost doubles. Doesn't it affect 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. OK. > >> 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).
OK. I see the patch series. Would it be applied to the mainline someday? I notice
that more than 5 months have passed since you sent the patch series.
Thanks.
> > Thanks, > > M. > > [1] https://lore.kernel.org/lkml/20201124141449.572446-1-maz@kernel.org/ >
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