Re: [PATCH 01/11] perf/x86: Fix native_perf_sched_clock_from_tsc() with __sched_clock_offset

[Peter Zijlstra]

On Wed, Feb 09, 2022 at 10:49:19AM +0200, Adrian Hunter wrote:
> native_perf_sched_clock_from_tsc() is used to produce a time value that can
> be consistent with perf_clock().  Consequently, it should be adjusted by
> __sched_clock_offset, the same as perf_clock() would be.
> 
> Fixes: 698eff6355f735 ("sched/clock, x86/perf: Fix perf test tsc")
> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> ---
>  arch/x86/kernel/tsc.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index a698196377be..c1c73fe324cd 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -242,7 +242,8 @@ u64 native_sched_clock(void)
>   */
>  u64 native_sched_clock_from_tsc(u64 tsc)
>  {
> -	return cycles_2_ns(tsc);
> +	return cycles_2_ns(tsc) +
> +	       (sched_clock_stable() ? __sched_clock_offset : 0);
>  }

Why do we care about the !sched_clock_stable() case?