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Description of problem: Today the cpufreq values provided in sys/devices/system/cpu/cpuX/ may be inaccurate when compared to a aperfmperf values. During the development of the updated hwcert cpuscaling for v7-1.4 aperfmperf was deemed to be the authoritative source of what speed is the core is actually running at. Steps to Reproduce: 1. compare aperfmperf calculation from aperf code provided by mjg to /sys cpuinfo_cur_freq and scaling_cur_freq values. Actual results: aperf and /sys show different values. Expected results: some /sys entry would show the same value as aperf. Additional info: TurboBoost/Core for example are not reflected in the current /sys values but appear in the aperf output.
The CPU frequency can change several times a second with the in-kernel automatic CPU speed governors. I would not be surprised to see different readings at different times. Exactly what kind of discrepancies are you seeing?
Example: This is on my laptop which is performing work (thunderbird, firefox, etc.) not similar to the test environment we should have on a v7 test box. [root@unused cpufreq]# pwd /sys/devices/system/cpu/cpu2/cpufreq [root@unused cpufreq]# cat cpuinfo_cur_freq 2701000 [root@unused cpufreq]# cat scaling_cur_freq 800000 [root@unused cpufreq]# ~rlandry/Downloads/aperf 2 Freq: 3.045GHz [root@unused cpufreq]# cpufreq-aperf CPU Average freq(KHz) Time in C0 Time in Cx C0 percentage 000 2511930 00 sec 003 ms 00 sec 996 ms 00 001 3214190 00 sec 931 ms 00 sec 068 ms 93 002 2971100 00 sec 737 ms 00 sec 262 ms 73 003 2917080 00 sec 153 ms 00 sec 846 ms 15 000 2809040 00 sec 571 ms 00 sec 428 ms 57 001 2538940 00 sec 291 ms 00 sec 708 ms 29 002 1458540 00 sec 200 ms 00 sec 799 ms 20 003 1404520 00 sec 227 ms 00 sec 772 ms 22 ^C [root@unused cpufreq]# cat scaling_governor userspace [root@unused cpufreq]# Today v7 uses mgj's aperf command as the authoritative value; though it is not part of the OS.
Since RHEL 6.3 External Beta has begun, and this bug remains unresolved, it has been rejected as it is not proposed as exception or blocker. Red Hat invites you to ask your support representative to propose this request, if appropriate and relevant, in the next release of Red Hat Enterprise Linux.
This feature has now been obsoleted by new hardware. The latest CPUs scale the frequency all by themselves, autonomously from the operating system. Statistics on how much of each frequency was used get exported through sysfs.