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Message-ID: <182553e4-a2e2-46f6-8c50-2de6f8effee7@efficios.com>
Date: Tue, 20 Feb 2024 20:19:32 -0500
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Subject: Re: [PATCH] sched/clock: Make local_clock() notrace
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To: Steven Rostedt <rostedt@goodmis.org>, LKML <linux-kernel@vger.kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
 Masami Hiramatsu <mhiramat@kernel.org>,
 Daniel Bristot de Oliveira <bristot@redhat.com>,
 Vincent Guittot <vincent.guittot@linaro.org>,
 Juri Lelli <juri.lelli@redhat.com>
References: <20240220202002.38fec245@gandalf.local.home>
From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
In-Reply-To: <20240220202002.38fec245@gandalf.local.home>
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On 2024-02-20 20:20, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> The "perf" clock in /sys/kernel/tracing/trace_clock enables local_clock(),
> where on machines that have CONFIG_HAVE_UNSTABLE_SCHED_CLOCK set is a
> normal function. This function can be traced.
> 
> I found that enabling the "perf" clock on some debug configs and running
> function tracer can live lock the machine. That is, it goes so slow that
> nothing moves forward.

And I bet this is why the try_cmpxchg for reservation was
looping endlessly. ;)

Thanks,

Mathieu

> 
> Cc: stable@vger.kernel.org
> Fixes: fb7d4948c4da2 ("sched/clock: Provide local_clock_noinstr()")
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>   kernel/sched/clock.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c
> index 3c6193de9cde..af8b698dee8c 100644
> --- a/kernel/sched/clock.c
> +++ b/kernel/sched/clock.c
> @@ -308,7 +308,7 @@ noinstr u64 local_clock_noinstr(void)
>   	return clock;
>   }
>   
> -u64 local_clock(void)
> +notrace u64 local_clock(void)
>   {
>   	u64 now;
>   	preempt_disable_notrace();

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com