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SubjectRe: [PATCH] arm64: don't account for cpu offline time with irqsoff tracer
On Wed, Sep 05, 2018 at 04:19:43PM +0800, Zhizhou Zhang wrote:
> 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@asrmicro.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

Hmm, so there are only a handful of other callers of stop_critical_timings()
which suggests that we probably shouldn't be calling this from deep in the
arch code. Do other architectures have the same problem? If not, how do they
avoid it?

Will

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