Paul Irofti:
> This also handles negative skew values that my prevoius diff did not.
> --- sys/arch/amd64/amd64/tsc.c
> +++ sys/arch/amd64/amd64/tsc.c
> @@ -216,6 +217,8 @@ tsc_get_timecount(struct timecounter *tc)
> void
> tsc_timecounter_init(struct cpu_info *ci, uint64_t cpufreq)
> {
> + CPU_INFO_ITERATOR cii;
> +
> #ifdef TSC_DEBUG
> printf("%s: TSC skew=%lld observed drift=%lld\n", __func__,
> (long long)ci->ci_tsc_skew, (long long)tsc_drift_observed);
> @@ -244,8 +247,16 @@ tsc_timecounter_init(struct cpu_info *ci, uint64_t
> cpufreq)
> printf("ERROR: %lld cycle TSC drift observed\n",
> (long long)tsc_drift_observed);
> tsc_timecounter.tc_quality = -1000;
> + tsc_timecounter.tc_user = 0;
> tsc_is_invariant = 0;
> }
> + CPU_INFO_FOREACH(cii, ci) {
> + if (ci->ci_tsc_skew < -TSC_SKEW_MAX ||
> + ci->ci_tsc_skew > TSC_SKEW_MAX) {
> + tsc_timecounter.tc_user = 0;
> + break;
> + }
> + }
>
> tc_init(&tsc_timecounter);
> }
If the output order from TSC_DEBUG in dmesg reflects the actual
execution order, then the relative call order is this:
cpu0 tsc_timecounter_init
cpu1 cpu_start_secondary
cpu1 tsc_timecounter_init
cpu2 cpu_start_secondary
cpu2 tsc_timecounter_init
cpu3 cpu_start_secondary
cpu3 tsc_timecounter_init
That CPU_INFO_FOREACH() loop would execute in the very first cpu0
tsc_timecounter_init() call, _before_ the skews of the other CPUs
are determined in the subsequent cpu_start_secondary() calls.
So, instead, I think the skew check needs to move to the top of
tsc_timecounter_init, where each secondary CPU checks its own skew
value and knocks out tsc_timecounter.tc_user if there is a problem.
Unless I'm misunderstanding the whole thing.
--
Christian "naddy" Weisgerber na...@mips.inka.de
