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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