linux-kernel - [PATCH] arm64: don't account for cpu offline time with irqsoff tracer

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Date:   Wed, 5 Sep 2018 16:19:43 +0800
From:   Zhizhou Zhang <zhizhouzhang@...micro.com>
To:     <catalin.marinas@....com>, <will.deacon@....com>,
        <james.morse@....com>, <julien.thierry@....com>,
        <dave.martin@....com>, <zhizhouzhang@...micro.com>,
        <suzuki.poulose@....com>, <sudeep.holla@....com>,
        <adobriyan@...il.com>, <lorenzo.pieralisi@....com>,
        <mark.rutland@....com>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH] arm64: don't account for cpu offline time with irqsoff tracer

This is no need to account for cpu offline time with irqsoff tracer.
We can trigger a large irqsoff latency with below commands:

$ echo irqsoff > /sys/kernel/debug/tracing/current_tracer
$ echo 0 > /sys/kernel/debug/tracing/options/function-trace
$ echo 1 > /sys/kernel/debug/tracing/tracing_on
$ echo 0 > /sys/devices/system/cpu/cpu1/online
$ # wait a while ...
$ echo 1 > /sys/devices/system/cpu/cpu1/online
$ cat /sys/kernel/debug/tracing/trace

Signed-off-by: Zhizhou Zhang <zhizhouzhang@...micro.com>
---
 arch/arm64/kernel/smp.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 25fcd22..faed8f6 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -346,6 +346,7 @@ void cpu_die(void)
 	idle_task_exit();
 
 	local_daif_mask();
+	stop_critical_timings();
 
 	/* Tell __cpu_die() that this CPU is now safe to dispose of */
 	(void)cpu_report_death();
-- 
1.9.1