linux-kernel - [PATCH v5 4/7] arm64: perf: Defer irq_work to IPI_IRQ

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Date:   Wed, 17 Jun 2020 12:38:48 +0100
From:   Alexandru Elisei <alexandru.elisei@....com>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     maz@...nel.org, will@...nel.org, catalin.marinas@....com,
        mark.rutland@....com, Julien Thierry <julien.thierry@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Will Deacon <will.deacon@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: [PATCH v5 4/7] arm64: perf: Defer irq_work to IPI_IRQ_WORK

From: Julien Thierry <julien.thierry@....com>

perf_event_overflow() can queue an irq_work on the current PE, which is
executed via an IPI. Move the processing of the irq_work from the PMU IRQ
handler to the IPI handler, which gets executed immediately afterwards.

This also makes the IRQ handler NMI safe, because it removes the call to
irq_work_run().

Cc: Julien Thierry <julien.thierry.kdev@...il.com>
Cc: Will Deacon <will.deacon@....com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>
Signed-off-by: Julien Thierry <julien.thierry@....com>
[Reworded commit]
Signed-off-by: Alexandru Elisei <alexandru.elisei@....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 a6195022be7d..cf1d92030790 100644
--- a/arch/arm64/kernel/perf_event.c
+++ b/arch/arm64/kernel/perf_event.c
@@ -750,20 +750,16 @@ 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();
-
 	return IRQ_HANDLED;
 }
 
-- 
2.27.0