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From: Julien Thierry <julien.thierry@arm.com>
To: Will Deacon <will@kernel.org>
Cc: mark.rutland@arm.com, peterz@infradead.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	will.deacon@arm.com, acme@kernel.org,
	alexander.shishkin@linux.intel.com, mingo@redhat.com,
	namhyung@kernel.org, sthotton@marvell.com, jolsa@redhat.com,
	linux-arm-kernel@lists.infradead.org, liwei391@huawei.com
Subject: Re: [PATCH v4 6/9] arm64: perf: Do not call irq_work_run in NMI context
Date: Fri, 2 Aug 2019 15:43:40 +0100
Message-ID: <429bfb7e-a07a-9c1d-97c1-aea846112c22@arm.com> (raw)
In-Reply-To: <20190801130611.n2xij2242ihxa5pr@willie-the-truck>



On 01/08/2019 14:06, Will Deacon wrote:
> On Wed, Jul 17, 2019 at 09:17:09AM +0100, Julien Thierry wrote:
>> Function irq_work_run is not NMI safe and should not be called from NMI
>> context.
>>
>> When PMU interrupt is an NMI do not call irq_work_run. Instead rely on the
>> IRQ work IPI to run the irq_work queue once NMI/IRQ contexts have been
>> exited.
>>
>> Signed-off-by: Julien Thierry <julien.thierry@arm.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>
>> ---
>>  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 0e2cf5d..9c959ad 100644
>> --- a/arch/arm64/kernel/perf_event.c
>> +++ b/arch/arm64/kernel/perf_event.c
>> @@ -776,20 +776,16 @@ 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();
> 
> What about the case where NMIs are not being used (e.g. GICv2)?
> 

As the comment above mentions. The overflow handler will trigger the
IPI_IRQ_WORK which will call the irq_work_run() both for NMI and normal IRQ.

Unless we really need to process the irq_work here, it makes things
simpler to get rid of the call.

It was suggested during the previous version:
https://www.spinics.net/lists/arm-kernel/msg740027.html

Cheers,

-- 
Julien Thierry

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  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-17  8:17 [PATCH v4 0/9] arm_pmu: Use NMI for perf interrupt Julien Thierry
2019-07-17  8:17 ` [PATCH v4 1/9] arm64: perf: avoid PMXEV* indirection Julien Thierry
2019-07-17  8:17 ` [PATCH v4 2/9] arm64: perf: Remove PMU locking Julien Thierry
2019-08-01 12:58   ` Will Deacon
2019-08-02 14:26     ` Julien Thierry
2019-07-17  8:17 ` [PATCH v4 3/9] arm: perf: save/resore pmsel Julien Thierry
2019-08-01 13:01   ` Will Deacon
2019-08-02 14:34     ` Julien Thierry
2019-07-17  8:17 ` [PATCH v4 4/9] arm: perf: Remove Remove PMU locking Julien Thierry
2019-08-01 13:06   ` Will Deacon
2019-08-02 14:36     ` Julien Thierry
2019-07-17  8:17 ` [PATCH v4 5/9] perf/arm_pmu: Move PMU lock to ARMv6 events Julien Thierry
2019-07-17  8:17 ` [PATCH v4 6/9] arm64: perf: Do not call irq_work_run in NMI context Julien Thierry
2019-08-01 13:06   ` Will Deacon
2019-08-02 14:43     ` Julien Thierry [this message]
2019-07-17  8:17 ` [PATCH v4 7/9] arm/arm64: kvm: pmu: Make overflow handler NMI safe Julien Thierry
2019-07-17  8:17 ` [PATCH v4 8/9] arm_pmu: Introduce pmu_irq_ops Julien Thierry
2019-07-17  8:17 ` [PATCH v4 9/9] arm_pmu: Use NMIs for PMU Julien Thierry
2019-07-30  9:11   ` Russell King - ARM Linux admin
2019-07-30  9:18     ` Julien Thierry
2019-07-30  9:28       ` Russell King - ARM Linux admin
2019-07-30 14:06         ` Julien Thierry
2019-07-17  9:02 ` [PATCH v4 0/9] arm_pmu: Use NMI for perf interrupt Julien Thierry
2019-07-30  9:05 ` Julien Thierry

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