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From: Will Deacon <will@kernel.org>
To: Stephen Boyd <swboyd@chromium.org>
Cc: Alexandru Elisei <alexandru.elisei@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, mark.rutland@arm.com,
	Julien Thierry <julien.thierry@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	maz@kernel.org, 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>,
	Jiri Olsa <jolsa@redhat.com>
Subject: Re: [PATCH v5 3/7] arm64: perf: Remove PMU locking
Date: Fri, 3 Jul 2020 14:45:16 +0100	[thread overview]
Message-ID: <20200703134515.GF18953@willie-the-truck> (raw)
In-Reply-To: <159255539947.62212.6059916295459835174@swboyd.mtv.corp.google.com>

On Fri, Jun 19, 2020 at 01:29:59AM -0700, Stephen Boyd wrote:
> Quoting Alexandru Elisei (2020-06-18 03:51:31)
> > The armv8pmu_{start,stop}() functions are called from the irq handler, so we're
> > safe from preemption in this case. They are also called via
> > pmu->pmu_{enable,disable} callbacks, and I didn't find an explicit contract
> > regarding preemption in include/linux/perf_event.h. I've checked the other call
> > sites, and I didn't find any instances where they are called with preemption
> > enabled, which makes sense as we don't want to disable the PMU on a another CPU by
> > accident.
> 
> If they're all callbacks then it's overkill to add this. Presumably it
> is better to enforce this wherever the callbacks are called from so as
> to not litter the callee with random cant_sleep() calls. Probably best
> to ignore my suggestion.
> 
> > 
> > I would be inclined to add cant_sleep() calls to armv8pmu_{start,stop}(). In the
> > previous iteration, there were WARN_ONs in these functions, and Will said [1] they
> > can be removed because they are per-CPU operations. Will, what do you think about
> > adding the lockdep assertions?
> > 
> > [1] https://www.spinics.net/lists/arm-kernel/msg745161.html
> > 
> 
> If I read it correctly Will is saying the same thing in that thread.

Right, in the cases where perf core already relies on things not being
preemptible, we don't need to add extra checks.

Will

  reply	other threads:[~2020-07-03 13:45 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
2020-06-18 10:51     ` Alexandru Elisei
2020-06-19  8:29       ` Stephen Boyd
2020-07-03 13:45         ` Will Deacon [this message]
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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