On Thu, 2014-05-29 at 21:16 -0400, Dave Jones wrote: > On Thu, May 29, 2014 at 06:07:16PM -0700, Tim Chen wrote: > > On Thu, 2014-05-29 at 19:54 -0400, George Spelvin wrote: > > > Sorry for the delay; my Ivy Bridge test machine isn't in my > > > office and getting to the console to tweak the BIOS is a > > > bit of a bother. > > > > > > Anyway, i7-4930K, turbo boost & hyperthreading disabled, > > > $ cat /sys/devices/system/cpu/cpu?/cpufreq/scaling_governor > > > performance > > > performance > > > performance > > > performance > > > performance > > > performance > > > > > > Oddly, though, CPU speed still seems to be fluctuating: > > > $ grep MHz /proc/cpuinfo > > > cpu MHz : 1255.875 > > > cpu MHz : 3168.375 > > > cpu MHz : 3062.125 > > > cpu MHz : 1468.375 > > > cpu MHz : 1309.000 > > > cpu MHz : 2212.125 > > > $ grep MHz /proc/cpuinfo > > > cpu MHz : 1255.875 > > > cpu MHz : 2690.250 > > > cpu MHz : 1255.875 > > > cpu MHz : 2530.875 > > > cpu MHz : 2212.125 > > > cpu MHz : 1521.500 > > > > This is odd. On my Ivy Bridge system the CPU speed from /proc/cpuinfo > > is at max freq once I set the performance governor. > > The numbers above almost look like > > the cpu frequency is fluctuating and an average is taken. > > What version of the kernel are you running? Is > > CONFIG_CPU_FREQ_GOV_PERFORMANCE compiled in? > > > > Does /sys/devices/system/cpu/cpu?/cpufreq/scaling_cur_freq > > also changes? > > > > Can you check what are the available governors in your system > > and available frequencies? > > > > cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_governors > > cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies > > > > If userspace governor is available, you can try set the governor > > to userspace, then pin frequency to 3400 MHz (assuming that's your > > max) with command like: > > intel_pstate overrides any governor choice you make through sysfs. > > Dave >
Dirk, Wonder if this the right behavior for intel_pstate that when I set the governor to performance, intel_pstate driver still adjusts the cpu frequencies around? Turbotstat also confirms that the frequencies are not at max, even though the max_perf_pct and min_perf_pct are both set at 100. I ran on my HSW system with 3.15-rc7 kernel and see similar issue that Geroge reported. It is really a pain when we need to do performance benchmarking and need to have a constant cpu frequency. Thanks. Tim -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
