Messages in this thread | | | Date | Tue, 17 Nov 2015 11:08:19 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [RFC PATCH -v2.1] x86: Kill notsc |
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On Tue, 17 Nov 2015, Borislav Petkov wrote: > On Tue, Nov 17, 2015 at 10:11:03AM +0100, Thomas Gleixner wrote: > > There is an interesting problem: > > > > tsc_init() > > { > > tsc_khz = x86_platform.calibrate_tsc(); > > if (!tsc_khz) { > > mark_tsc_unstable("could not calculate TSC khz"); > > ... > > } > > > > In the current code we do NOT use TSC for sched_clock() and that's > > correct as we have no idea what the TSC frequency is. > > > > With your changes that is not longer the case, so you end up with a > > completely wreckaged sched clock. > > Hmm, I see it. > > Well, I had a related splat which bombed because cyc2ns_init() had to > run before we do sched_init()->idle_init() which called sched_clock() > and there we did the cycles_2_ns() thing and the percpu vars weren't > initialized yet. > > That's why I did this: > > +void __init early_tsc_init(void) > +{ > + int cpu; > + > + /* > + * We need to init the cycles to ns conversion machinery because > + * init_idle() below will call sched_clock() which needs it. > + */ > + for_each_possible_cpu(cpu) > + cyc2ns_init(cpu); > +} > > Maybe I should move tsc_init() before sched_init() so that the > calibration happens before we use the TSC in sched_clock() for the first > time...?
How does that help if your TSC frequency is 0 after the calibration?
Thanks,
tglx
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