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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, liwei391@huawei.com,
	will.deacon@arm.com, Russell King <linux@armlinux.org.uk>,
	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
Subject: Re: [PATCH v4 4/9] arm: perf: Remove Remove PMU locking
Date: Fri, 2 Aug 2019 15:36:17 +0100
Message-ID: <613ebf21-2761-c045-f30d-c1893c3e235e@arm.com> (raw)
In-Reply-To: <20190801130640.4ed5bcy2rdgdtztq@willie-the-truck>



On 01/08/2019 14:06, Will Deacon wrote:
> [extra 'Remove' in subject]
> 
> On Wed, Jul 17, 2019 at 09:17:07AM +0100, Julien Thierry wrote:
>> Since the PMU interrupt saves and restores the value of the selector
>> register, there is no need to serialize register accesses against the
>> interrupt contexts.
>>
>> For operations that can be called with interrupts enabled, preemption
>> still needs to be disabled to ensure the programming of the PMU is
>> done on the expected CPU and not migrated mid-programming.
>>
>> 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: Russell King <linux@armlinux.org.uk>
>> ---
>>  arch/arm/kernel/perf_event_v7.c | 54 ++---------------------------------------
>>  1 file changed, 2 insertions(+), 52 deletions(-)
> 
> I'm struggling to see why this patch is needed or, if it is, why we're not
> doing something similar for v6 and xscale.

We can't do a similar things for v6 because it doesn't have set/clear
registers for event enabling/disabling. To do that on v6 we must do
read-modify-write, so we need to keep a spinlock.

For v7 we can do without it.

Thanks,

-- 
Julien Thierry

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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 [this message]
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
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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