Re: [PATCH] sched/clock: Make local_clock() notrace

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

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