Messages in this thread | | | Date | Tue, 17 Nov 2015 10:33:09 +0100 | From | Borislav Petkov <> | Subject | Re: [RFC PATCH -v2.1] x86: Kill notsc |
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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...?
-- Regards/Gruss, Boris.
ECO tip #101: Trim your mails when you reply.
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