Messages in this thread | | | Date | Mon, 13 Mar 2017 20:04:14 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: x86/tsc: Fix ART for TSC_KNOWN_FREQ |
| |
On Mon, 13 Mar 2017, Peter Zijlstra wrote:
> > Subhransu reported that convert_art_to_tsc() isn't working for him. > > It turns out that because of commit: > > 57779dc2b3b7 ("x86, tsc: Skip refined tsc calibration on systems with reliable TSC")
That's the wrong culprit. The problem was introduced with the ART support patches. I fixed the changelog up.
> Systems with TSC_KNOWN_FREQ (due to having CPUID.15h) will not run the > refined calibration thing, and then forget to set the ART clocksource > relation. > > We cannot set the ART relation prior to running the refined calibration; > therefore duplicate the lines. > > XXX: should we clear this in mark_tsc_unstable() ?
It's already handled. get_device_system_timestamp() which convert ART to clock monotonic checks whether the timekeeper clocksource is the same as the correlated ART clocksource, i.e. TSC. So when timekeeping switches away from TSC get_device_system_timestamp() returns -ENODEV.
Thanks,
tglx
| |