Messages in this thread | | | Date | Mon, 22 Jun 2020 15:19:18 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH v5 4/7] arm64: perf: Defer irq_work to IPI_IRQ_WORK |
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On Wed, Jun 17, 2020 at 12:38:48PM +0100, Alexandru Elisei wrote: > From: Julien Thierry <julien.thierry@arm.com> > > perf_event_overflow() can queue an irq_work on the current PE, which is > executed via an IPI. Move the processing of the irq_work from the PMU IRQ > handler to the IPI handler, which gets executed immediately afterwards. > > This also makes the IRQ handler NMI safe, because it removes the call to > irq_work_run().
It wasn't entirely clear to me what the situation was today, and why this was sound. How about the following to spell that out more explicitly:
| When handling events armv8pmu_handle_irq() calls | perf_event_overflow(), and subsequently calls irq_work_run() to handle | any work queued by perf_event_overflow(). As perf_event_overflow() | raises IPI_IRQ_WORK when queing the work, this isn't strictly | necessary and the work could be handled as part of the IPI_IRQ_WORK | handler. | | In the common case the IPI handler will run immediately after the PMU | IRQ handler, and where the PE is heavily loaded with interrupts other | handlers may run first, widening the window where some counters are | disabled. | | In practice this window is unlikely to be a significant issue, and | removing the call to irq_work_run() would make the PMU IRQ handler NMI | safe in addition to making it simpler, so let's do that.
Thanks, Mark.
> > Cc: Julien Thierry <julien.thierry.kdev@gmail.com> > Cc: Will Deacon <will.deacon@arm.com> > Cc: Mark Rutland <mark.rutland@arm.com> > Cc: Peter Zijlstra <peterz@infradead.org> > Cc: Ingo Molnar <mingo@redhat.com> > Cc: Arnaldo Carvalho de Melo <acme@kernel.org> > Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> > Cc: Jiri Olsa <jolsa@redhat.com> > Cc: Namhyung Kim <namhyung@kernel.org> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Signed-off-by: Julien Thierry <julien.thierry@arm.com> > [Reworded commit] > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com> > --- > arch/arm64/kernel/perf_event.c | 14 +++++--------- > 1 file changed, 5 insertions(+), 9 deletions(-) > > diff --git a/arch/arm64/kernel/perf_event.c b/arch/arm64/kernel/perf_event.c > index a6195022be7d..cf1d92030790 100644 > --- a/arch/arm64/kernel/perf_event.c > +++ b/arch/arm64/kernel/perf_event.c > @@ -750,20 +750,16 @@ static irqreturn_t armv8pmu_handle_irq(struct arm_pmu *cpu_pmu) > if (!armpmu_event_set_period(event)) > continue; > > + /* > + * Perf event overflow will queue the processing of the event as > + * an irq_work which will be taken care of in the handling of > + * IPI_IRQ_WORK. > + */ > if (perf_event_overflow(event, &data, regs)) > cpu_pmu->disable(event); > } > armv8pmu_start(cpu_pmu); > > - /* > - * Handle the pending perf events. > - * > - * Note: this call *must* be run with interrupts disabled. For > - * platforms that can have the PMU interrupts raised as an NMI, this > - * will not work. > - */ > - irq_work_run(); > - > return IRQ_HANDLED; > } > > -- > 2.27.0 >
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