Greetings,
It's looking like my Q6600 is kinda slow at switching gears, and I'd
just like to verify that it is the hardware, not something odd going on
in cpuidle territory.
If I boot idle=poll and set scaling_governor to performance, the CPU is
running full bore (2.4GHz) per both cpufreq and turbostat, and jitter is
~10 usecs (~5 usecs on non-rt kernel)
If I boot processor.max_cstate=1 instead, to have _some_ power saving,
set the governor to performance and measure, I notice that while cpufreq
swears my CPU is locked in at 2.4GHz, turbostat says cpufreq is lying to
me, that my CPUs _are_ changing frequency, bouncing around a bit.
If I switch to powersave, there is no frequency shifting, and little
jitter. Switch to performance and there's much jitter, until I add a
cpu hog, then CPU goes to full throttle, and jitter goes away.
This large jitter differential does not happen on a L5520 box, or a few
others I've tested with much nicer CPUs than mine, which leads me to
suspect that my Q6600's oldish two speed gearbox has straight cut gears
and no synchros, it's double-clutching, and that takes a while ;-)
Kernel: v2.6.33.6-rt26-17-g911d28c processor.max_cstate=1
Box: Q6600
cset shield --cpu 1-3 -k on
marge:/root/tmp # ./periodic_timer -p40 -c3 -f60 -t1 -s -T -F2392.594 -C1000
Pinned to CPU3 priority: 40 timer freq: 60 Hz tolerance: 1 usecs, stats interval: 1000 samples
measurement clock; TSC @2392.594MHz
period: 16666.67 usecs min: 16552.33 max: 16772.62 mean: 16667.12 stddev: 5.72
585 > 1 usec errors min: -105.95 max: 114.34 mean: -0.48 stddev: 28.12
period: 16666.67 usecs min: 16549.42 max: 16783.26 mean: 16667.13 stddev: 6.30
589 > 1 usec errors min: -116.59 max: 117.25 mean: -0.51 stddev: 36.58
start SCHED_OTHER cpu hog on CPU3 (or even better boot idle=poll)
period: 16666.67 usecs min: 16662.84 max: 16676.36 mean: 16667.10 stddev: 0.37
15 > 1 usec errors min: -9.69 max: 3.83 mean: -0.93 stddev: 3.75
period: 16666.67 usecs min: 16663.89 max: 16674.49 mean: 16667.10 stddev: 0.30
11 > 1 usec errors min: -7.82 max: 2.78 mean: -1.02 stddev: 3.40
--
To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
