https://bugzilla.kernel.org/show_bug.cgi?id=30712 Summary: Slow transitioning AMD ondemand CPU because of wrong sampling_rate Product: Power Management Version: 2.5 Kernel Version: 2.6.37 Platform: All OS/Version: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: cpufreq AssignedTo: cpufreq@xxxxxxxxxxxxxxx ReportedBy: justincase@xxxxxxxxxxx Regression: No This bug has been previously reported on the Debian bugtracker, please have a look at http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=614256 as it contains much more information. Using the ondemand governor, the time taken for the CPU to rise to max frequency is noticeable by the user and impact global performance. Setting sampling_rate to sampling_rate_min makes the the CPU perform much faster transitions. On this processor : AMD Athlon(tm) 64 X2 Dual Core Processor 4200+ Down freq: 1000MHz / Up freq: 2200MHz I have: /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate:109000 /sys/devices/system/cpu/cpufreq/ondemand/sampling_rate_min:10900 /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_transition_latency:109000 This simple command solves the problem: cat sampling_rate_min >| sampling_rate So, I suppose the default values are not optimal. In contrast, I have an Intel(R) Core(TM)2 Duo CPU T7250 @ 2.00GHz, and the three values mentioned above are all equal to 10000 on this processor. I did some dirty benchmarking using the following command: dd if=/dev/zero of=/dev/null bs=300k count=1000 Here are my results in GB/s (several averages) for the AMD CPU: -------------- performance : 7.61 / 7.61 / 7.61 / 7.56 / 7.37 ondemand (no-tweaking) : 4.83 / 4.68 / 4.73 / 5.14 / 5.51 / 5.37 ondemand (sampling_rate = rampling_rate_min, i.e. default/10) : 7.00 / 7.07 / 7.03 / 7.06 / 7.02 / 7.01 / 7.04 -------------- Please see the original Debian bug report for more information. Thanks -- Configure bugmail: https://bugzilla.kernel.org/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug. -- To unsubscribe from this list: send the line "unsubscribe cpufreq" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
