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    SubjectRe: [PATCH 5/5] cpufreq: Add support for actual freq
    From: Thomas Renninger <trenn@suse.de>
    Date: Tue, Mar 23, 2010 at 12:51:18PM +0100

    Hi,

    > scaling_cur freq should show the frequency the kernel/cpufreq
    > subsystem thinks it's in.

    Well, we have also
    /sys/devices/system/cpu/cpu<NUM>/cpufreq/cpuinfo_cur_freq and it reads
    also policy->cur. Why not show the actual frequency in scaling_cur_freq
    then?

    > You show the average freq and the time of the measured average
    > frequency depends on when the cpufreq subsystem called getavg()
    > the last time.
    > Also the time frame of the average freq the cpufreq subsystem
    > gets when calling getavg() now depends on whether and how often
    > userspace calls scaling_cur_freq which influences switching policy.
    >
    > Latest cpufrequtils (ver 006) supports cpufreq-aperf to check whether
    > cores enter boost mode. Len Brown afaik also has a userspace tool, but
    > if it has any advantages, it should IMO get integrated into cpufrequtils
    > which people know to use when looking at cpufreq.
    >
    > I once thought about adding scaling_avg_freq which gets an own
    > aperf_mperf counter, but you don't know whether another app read out the
    > average freq in between and your expected measured time frame is wrong then.
    > You could remember aperf/mperf per pid and free the saved aperf/mperf value
    > if the process dies..., but what for if this can be read out in userspace.

    Ah yes, I see what you mean. Yet, I still don't like the idea of having
    to use a special userspace tool just to read the actual frequency. How
    about we hook into <drivers/cpufreq/cpufreq_ondemand.c:dbs_check_cpu()>
    and passively output the freq_avg after being computed in

    freq_avg = __cpufreq_driver_getavg(policy, j);
    if (freq_avg <= 0)
    freq_avg = policy->cur;

    through sysfs. Hmm...?

    --
    Regards/Gruss,
    Boris.

    --
    Advanced Micro Devices, Inc.
    Operating Systems Research Center


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