My Dell Latitude E7440 seems to occassionally enter periods where the CPU clockrate of all cores (as shown by cpupower and powertop) is stuck in the few-hundred-MHz range even under load. Often this is around 600 MHz. At the moment I'm running 3.17-rc5 although I believe I have observed similar behavior even under older kernels. I'm afraid I don't have a reliable technique for reproducing the issue although it may be correlated with S3 suspend. Various If under load for long enough (several minutes) it seems it will eventually clock back up to 2.0GHz. However, if I then kill the load it will clock back down to 600MHz (as expected) and remain there until again subjected to prolonged load. I've attached a tarball with output from the various performance monitoring tools (cpupower and turbostat) for several sets of conditions, * while the machine is idle (v3.15-rc5-idle) * while the machine is under load (provided by stress -c4) and clocked at around 600 MHz (v3.15-rc5-loaded) * after the machine has been load for roughly 3.5 minutes and has finally clocked up to 2 GHz. Oddly it doesn't make it above 2.0GHz despite cpuinfo_max_freq being 2.9GHz. (v3.15-rc5-loaded2) Looking through sysfs I found the following a bit odd, $ for i in /sys/devices/system/cpu/cpu0/cpufreq/*; do echo $i $(sudo cat $i); done cpufreq/affected_cpus 0 cpufreq/cpuinfo_cur_freq 628906 cpufreq/cpuinfo_max_freq 2900000 cpufreq/cpuinfo_min_freq 800000 cpufreq/cpuinfo_transition_latency 4294967295 cpufreq/related_cpus 0 cpufreq/scaling_available_governors performance powersave cpufreq/scaling_driver intel_pstate cpufreq/scaling_governor powersave cpufreq/scaling_max_freq 2900000 cpufreq/scaling_min_freq 800000 cpufreq/scaling_setspeed <unsupported> Note the peculiar value of cpuinfo_transition_latency. Seems just a tad long.
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Oh dear, somehow these messages never made it to my inbox. My apologies for the noise. Unfortunately I've since deleted the file I had meant to attach and cannot reproduce the issue at the moment. This may either be due to a firmware upgrade or the lower temperatures of winter. I'll re-open if the issue again comes up this summer.