> >> Frequency transition now occurs during the thread switching if the
> >> cmt_utilization
> >> of the power active domain think it's necessary.
> >> It's(event-mode) much more sensitive than before(poll-mode), even "kstat |
> >> grep
> >> current_clock_Hz" is possible to trigger a frequency transition. So, now,
> >> powertop
> >> is more reliable to report the cpu frequency utilization.
> >
> > The "P-states (frequencies)" statistic of powertop is showing
> > four entries (996, 1328, 1660 and 1992 MHz on a C2D T7200),
> > and I see either 100% at 996 Mhz, or 100% at 1992 MHz.
> >
> > That it doesn't use the 1328 and 1660 Mhz frequencies
> > is already reported as bug 6808377 "event based CPUPM
> > could leverage mid range speeds".
>
> Yeah, exactly by the current design.
>
> >
> > But why is it always reporting a frequency usage split for 996
> > and 1992 MHz as 100% - 0% (or 0% - 100%) ? Somehow it
> > doesn't make sense that in event-mode (according to powertop)
> > the cpu is always running at the slowest (highest) speed during
> > the 5 second powertop sample interval.
>
> I attached a dtrace probe for your interest, which is exactly what powertop
> is currently using.
> I actually saw some mid value on the 16 logical cores system.
It's a bug in powertop. The dtrace code that powertop is using
aggregates on a processorid_t (cpu) and an uint32_t (cpuspeed).
But in function pt_cpufreq_dtrace_walk() the cpu speed is
read as uint64_t - this is working with bogus values for cpu
speed!
Suggested fix:
diff --git a/usr/src/cmd/powertop/common/cpufreq.c
b/usr/src/cmd/powertop/common/cpufreq.c
--- a/usr/src/cmd/powertop/common/cpufreq.c
+++ b/usr/src/cmd/powertop/common/cpufreq.c
@@ -431,7 +431,7 @@ pt_cpufreq_dtrace_walk(const dtrace_aggd
dtrace_recdesc_t *cpu_rec, *speed_rec;
cpu_power_info_t *cpu_pow;
int32_t cpu;
- uint64_t speed;
+ uint32_t speed;
hrtime_t dt_state_time = 0;
int i;
@@ -447,7 +447,7 @@ pt_cpufreq_dtrace_walk(const dtrace_aggd
/* LINTED - alignment */
cpu = *(int32_t *)(data->dtada_data + cpu_rec->dtrd_offset);
/* LINTED - alignment */
- speed = *(uint64_t *)(data->dtada_data +
+ speed = *(uint32_t *)(data->dtada_data +
speed_rec->dtrd_offset);
if (speed == 0) {
--
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