Re: [PATCH] x86/tsc: Have tsc=recalibrate override things

Peter Zijlstra
2023-10-30T16:04:37Z

On Mon, Oct 30, 2023 at 05:00:50PM +0100, Peter Zijlstra wrote:
> ---
> arch/x86/kernel/tsc.c | 26 +++++++++++++-------------
> 1 file changed, 13 insertions(+), 13 deletions(-)
>
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> index 15f97c0abc9d..ebca304ecea0 100644
> --- a/arch/x86/kernel/tsc.c
> +++ b/arch/x86/kernel/tsc.c
> @@ -1430,14 +1430,13 @@ static void tsc_refine_calibration_work(struct work_struct *work)
> hpet ? "HPET" : "PM_TIMER",
> (unsigned long)freq / 1000,
> (unsigned long)freq % 1000);
> + } else {
>
> - return;
> + /* Make sure we're within 1% */
> + if (abs(tsc_khz - freq) > tsc_khz/100)
> + goto out;
> }
>
> - /* Make sure we're within 1% */
> - if (abs(tsc_khz - freq) > tsc_khz/100)
> - goto out;
> -
> tsc_khz = freq;
> pr_info("Refined TSC clocksource calibration: %lu.%03lu MHz\n",
> (unsigned long)tsc_khz / 1000,
> @@ -1475,18 +1474,19 @@ static int __init init_tsc_clocksource(void)
> if (boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3))
> clocksource_tsc.flags |= CLOCK_SOURCE_SUSPEND_NONSTOP;
>
> - /*
> - * When TSC frequency is known (retrieved via MSR or CPUID), we skip
> - * the refined calibration and directly register it as a clocksource.
> - */
> if (boot_cpu_has(X86_FEATURE_TSC_KNOWN_FREQ)) {
> if (boot_cpu_has(X86_FEATURE_ART))
> art_related_clocksource = &clocksource_tsc;
> - clocksource_register_khz(&clocksource_tsc, tsc_khz);
> - clocksource_unregister(&clocksource_tsc_early);
>
> - if (!tsc_force_recalibrate)
> - return 0;
> + /*
> + * When TSC frequency is known (retrieved via MSR or CPUID), we
> + * skip the refined calibration and directly register it as a
> + * clocksource.
> + */
> + if (!tsc_force_recalibrate) {
> + clocksource_register_khz(&clocksource_tsc, tsc_khz);
> + clocksource_unregister(&clocksource_tsc_early);

+ return 0;

Clearly I should step away from the keyboard now.

> + }
> }
>
> schedule_delayed_work(&tsc_irqwork, 0);
>