linux-kernel - [RFC] per-CPU usage in perf core-book3s

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Message-ID: <20200127150620.taio2txyqreg4kn6@linutronix.de>
Date:   Mon, 27 Jan 2020 16:06:20 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: [RFC] per-CPU usage in perf core-book3s

I've been looking at usage of per-CPU variable cpu_hw_events in
arch/powerpc/perf/core-book3s.c.

power_pmu_enable() and power_pmu_disable() (pmu::pmu_enable() and
pmu::pmu_disable()) are accessing the variable and the callbacks are
invoked always with disabled interrupts.

power_pmu_event_init() (pmu::event_init()) is invoked from preemptible
context and uses get_cpu_var() to obtain a stable pointer (by disabling
preemption).

pmu::pmu_enable() and pmu::pmu_disable() can be invoked via a hrtimer
(perf_mux_hrtimer_handler()) and it invokes pmu::pmu_enable() and
pmu::pmu_disable() as part of the callback.

Is there anything that prevents the timer callback to interrupt
pmu::event_init() while it is accessing per-CPU data?

Sebastian