https://bugzilla.kernel.org/show_bug.cgi?id=54761 Summary: Variable cpu frequency causes to loose performance Product: Power Management Version: 2.5 Kernel Version: Ubuntu 3.8.0-9.18-generic 3.8.1 Platform: All OS/Version: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: cpufreq AssignedTo: cpufreq@xxxxxxxxxxxxxxx ReportedBy: sworddragon2@xxxxxxx Regression: No Created an attachment (id=94381) --> (https://bugzilla.kernel.org/attachment.cgi?id=94381) Example application In my sytsme is an AMD Phenom II X6 1045T with 6 cores and a scaling frequency of "2700000 2000000 1400000 800000". I have noticed if a process is using ~the half of cpu time of a core I'm getting heavy performance impacts if I'm using the ondemand governor. Switching to the performance governor solves this problem. I have written a testcase in C which demonstrates this problem (compiled with "gcc -o governor governor.c -lpthread"). The application creates 20 threads (change NUM_THREADS in the code if needed) - every of them uses only a little of cpu time. All threads will be executed on the same core. Here are the differences between both governors: ondemand: The frequency of the related core goes up to 1400 MHz and the used cpu time of this core is ~50%. The application needs ~7.17 seconds to be finished. performance: The frequency of the related core is constantly 2700 MHz and the used cpu time of this core is ~25%. The application needs ~5.99 seconds to be finished. The difference between the used cpu time is logical since the frequency is as double so high. But both runs are far away from a 100% usage so theoretically they should be as same fast. -- 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
