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From: Stephen Boyd <swboyd@chromium.org>
To: Alexandru Elisei <alexandru.elisei@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Cc: mark.rutland@arm.com, Julien Thierry <julien.thierry@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	maz@kernel.org, Jiri Olsa <jolsa@redhat.com>,
	Will Deacon <will.deacon@arm.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Ingo Molnar <mingo@redhat.com>,
	catalin.marinas@arm.com, Namhyung Kim <namhyung@kernel.org>,
	will@kernel.org
Subject: Re: [PATCH v5 3/7] arm64: perf: Remove PMU locking
Date: Wed, 17 Jun 2020 13:17:12 -0700	[thread overview]
Message-ID: <159242503203.62212.1690942414916053920@swboyd.mtv.corp.google.com> (raw)
In-Reply-To: <20200617113851.607706-4-alexandru.elisei@arm.com>

Quoting Alexandru Elisei (2020-06-17 04:38:47)
> From: Julien Thierry <julien.thierry@arm.com>
> 
> The PMU is disabled and enabled, and the counters are programmed from
> contexts where interrupts or preemption is disabled.
> 
> The functions to toggle the PMU and to program the PMU counters access the
> registers directly and don't access data modified by the interrupt handler.
> That, and the fact that they're always called from non-preemptible
> contexts, means that we don't need to disable interrupts or use a spinlock.

Maybe we should add a lockdep assertion that the code isn't preemptible?
I.e. add a cant_sleep() call? Or is it more that we don't need locking
because we're just doing register accesses and don't need to protect
those accesses from each other?

  reply	other threads:[~2020-06-17 20:17 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-17 11:38 [PATCH v5 0/7] arm_pmu: Use NMI for perf interrupt Alexandru Elisei
2020-06-17 11:38 ` [PATCH v5 1/7] arm64: perf: Add missing ISB in armv8pmu_enable_event() Alexandru Elisei
2020-06-17 20:01   ` Stephen Boyd
2020-06-18 10:50     ` Alexandru Elisei
2020-06-17 11:38 ` [PATCH v5 2/7] arm64: perf: Avoid PMXEV* indirection Alexandru Elisei
2020-06-17 20:11   ` Stephen Boyd
2020-06-18 10:51     ` Alexandru Elisei
2020-06-19  8:26       ` Stephen Boyd
2020-06-17 11:38 ` [PATCH v5 3/7] arm64: perf: Remove PMU locking Alexandru Elisei
2020-06-17 20:17   ` Stephen Boyd [this message]
2020-06-18 10:51     ` Alexandru Elisei
2020-06-19  8:29       ` Stephen Boyd
2020-07-03 13:45         ` Will Deacon
2020-06-17 11:38 ` [PATCH v5 4/7] arm64: perf: Defer irq_work to IPI_IRQ_WORK Alexandru Elisei
2020-06-22 14:19   ` Mark Rutland
2020-06-23  9:47     ` Alexandru Elisei
2020-06-17 11:38 ` [PATCH v5 5/7] arm64: kvm: pmu: Make overflow handler NMI safe Alexandru Elisei
2020-06-17 11:38 ` [PATCH v5 6/7] arm_pmu: Introduce pmu_irq_ops Alexandru Elisei
2020-06-17 20:23   ` Stephen Boyd
2020-06-18 10:51     ` Alexandru Elisei
2020-06-19  8:33       ` Stephen Boyd
2020-06-17 11:38 ` [PATCH v5 7/7] arm_pmu: arm64: Use NMIs for PMU Alexandru Elisei
2020-06-25 15:11 ` [PATCH v5 0/7] arm_pmu: Use NMI for perf interrupt Alexandru Elisei

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