On Fri, Dec 15, 2023 at 11:06:07PM +0100, Peter Hilber wrote:
> Add a clocksource ID for TSC and a distinct one for the early TSC.
>
> Use distinct IDs for TSC and early TSC, since those also have distinct
> clocksource structs. This should help to keep existing semantics when
> comparing clocksources.
>
> Also, set the recently added struct system_counterval_t member cs_id to the
> TSC ID in the cases where the clocksource member is being set to the TSC
> clocksource. In the future, this will keep get_device_system_crosststamp()
> working, when it will compare the clocksource id in struct
> system_counterval_t, rather than the clocksource.
>
> For the x86 ART related code, system_counterval_t.cs == NULL corresponds to
> system_counterval_t.cs_id == CSID_GENERIC (0).
>
> Signed-off-by: Peter Hilber <peter.hilber@xxxxxxxxxxxxxxx>
Hi Peter,
some minor feedback from my side that you may consider for
a future revision.
> diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
...
> @@ -1327,12 +1334,15 @@ EXPORT_SYMBOL(convert_art_to_tsc);
> * that this flag is set before conversion to TSC is attempted.
> *
> * Return:
> - * struct system_counterval_t - system counter value with the pointer to the
> + * struct system_counterval_t - system counter value with the ID of the
> * corresponding clocksource
> * @cycles: System counter value
> * @cs: Clocksource corresponding to system counter value. Used
> * by timekeeping code to verify comparability of two cycle
> * values.
> + * @cs_id: Clocksource ID corresponding to system counter value.
> + * Used by timekeeping code to verify comparability of two
> + * cycle values.
None of the documented parameters to convert_art_ns_to_tsc() above
correspond to the parameters of convert_art_ns_to_tsc() below.
I would suggest a separate patch to address this.
And dropping this hunk from this patch.
The same patch that corrects the kernel doc for convert_art_ns_to_tsc()
could also correct the kernel doc for tsc_refine_calibration_work()
by documenting it's work parameter.
> */
>
> struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns)
> @@ -1347,8 +1357,11 @@ struct system_counterval_t convert_art_ns_to_tsc(u64 art_ns)
> do_div(tmp, USEC_PER_SEC);
> res += tmp;
>
> - return (struct system_counterval_t) { .cs = art_related_clocksource,
> - .cycles = res};
> + return (struct system_counterval_t) {
> + .cs = art_related_clocksource,
> + .cs_id = have_art ? CSID_X86_TSC : CSID_GENERIC,
> + .cycles = res
> + };
> }
> EXPORT_SYMBOL(convert_art_ns_to_tsc);
>
> @@ -1454,8 +1467,10 @@ static void tsc_refine_calibration_work(struct work_struct *work)
> if (tsc_unstable)
> goto unreg;
>
> - if (boot_cpu_has(X86_FEATURE_ART))
> + if (boot_cpu_has(X86_FEATURE_ART)) {
> art_related_clocksource = &clocksource_tsc;
> + have_art = true;
> + }
> clocksource_register_khz(&clocksource_tsc, tsc_khz);
> unreg:
> clocksource_unregister(&clocksource_tsc_early);
...
