Messages in this thread | | | Date | Tue, 26 Jun 2018 17:42:14 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH v12 09/11] x86/tsc: prepare for early sched_clock |
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Pavel,
first of all, sorry for my last outburst. I just was in a lousy mood after staring into too much half baken stuff and failed to make myself stay away from the computer.
On Sun, 24 Jun 2018, Thomas Gleixner wrote: > On Sat, 23 Jun 2018, Pavel Tatashin wrote: > And this early init sequence also needs to pull over the tsc adjust > magic. So tsc_early_delay_calibrate() which should btw. be renamed to > tsc_early_init() should have: > > { > cpu_khz = x86_platform.calibrate_cpu(); > tsc_khz = x86_platform.calibrate_tsc(); > > tsc_khz = tsc_khz ? : cpu_khz; > if (!tsc_khz) > return; > > /* Sanitize TSC ADJUST before cyc2ns gets initialized */ > tsc_store_and_check_tsc_adjust(true); > > calc_lpj(tsc_khz); > > tsc_sched_clock_init(); > }
Peter made me look deeper into this and there are a few issues, which I missed, depending on when some of the resources become available. So we probably cannot hook all of this into tsc_early_delay_calibrate().
I have an idea how to distangle it and we'll end up in a staged approach, which looks like this:
1) Earliest one (not sure how early yet)
Attempt to use MSR/CPUID. If not running on a hypervisor this can try the quick PIT calibration, but nothing else.
2) Post init_hypervisor_platform()
An attempt to use the hypervisor data can be made.
3) Post early_acpi_boot_init()
This can do PIT/HPET based calibration
4) Post x86_dtb_init()
PIT/PMTIMER based calibration
Once tsc_khz is known, no further attempts of calibration are made. I'll look into that later tonight.
Thanks,
tglx
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