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    Subject[PATCH 1/7] CPUFREQ: Introduce /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_transition_latency
    Date
    It's not only useful for the ondemand and conservative governors, but
    also for userspace daemons to know about the HW transition latency of
    the CPU.
    It is especially useful for userspace to know about this value when
    the ondemand or conservative governors are run. The sampling rate
    control value depends on it and for userspace being able to set sane
    tuning values there it has to know about the transition latency.

    Signed-off-by: Thomas Renninger <trenn@suse.de>
    ---
    Documentation/cpu-freq/user-guide.txt | 12 ++++++++++++
    drivers/cpufreq/cpufreq.c | 3 +++
    2 files changed, 15 insertions(+), 0 deletions(-)

    diff --git a/Documentation/cpu-freq/user-guide.txt b/Documentation/cpu-freq/user-guide.txt
    index e3443dd..57f23cb 100644
    --- a/Documentation/cpu-freq/user-guide.txt
    +++ b/Documentation/cpu-freq/user-guide.txt
    @@ -152,6 +152,18 @@ cpuinfo_min_freq : this file shows the minimum operating
    frequency the processor can run at(in kHz)
    cpuinfo_max_freq : this file shows the maximum operating
    frequency the processor can run at(in kHz)
    +cpuinfo_transition_latency The time it takes on this CPU to
    + switch between two frequencies in nano
    + seconds. If unknown or known to be
    + that high that the driver does not
    + work with the ondemand governor, -1
    + (CPUFREQ_ETERNAL) will be returned.
    + Using this information can be useful
    + to choose an appropriate polling
    + frequency for a kernel governor or
    + userspace daemon. Make sure to not
    + switch the frequency too often
    + resulting in performance loss.
    scaling_driver : this file shows what cpufreq driver is
    used to set the frequency on this CPU

    diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
    index b55cb67..ae92986 100644
    --- a/drivers/cpufreq/cpufreq.c
    +++ b/drivers/cpufreq/cpufreq.c
    @@ -455,6 +455,7 @@ static ssize_t show_##file_name \

    show_one(cpuinfo_min_freq, cpuinfo.min_freq);
    show_one(cpuinfo_max_freq, cpuinfo.max_freq);
    +show_one(cpuinfo_transition_latency, cpuinfo.transition_latency);
    show_one(scaling_min_freq, min);
    show_one(scaling_max_freq, max);
    show_one(scaling_cur_freq, cur);
    @@ -660,6 +661,7 @@ __ATTR(_name, 0644, show_##_name, store_##_name)
    define_one_ro0400(cpuinfo_cur_freq);
    define_one_ro(cpuinfo_min_freq);
    define_one_ro(cpuinfo_max_freq);
    +define_one_ro(cpuinfo_transition_latency);
    define_one_ro(scaling_available_governors);
    define_one_ro(scaling_driver);
    define_one_ro(scaling_cur_freq);
    @@ -673,6 +675,7 @@ define_one_rw(scaling_setspeed);
    static struct attribute *default_attrs[] = {
    &cpuinfo_min_freq.attr,
    &cpuinfo_max_freq.attr,
    + &cpuinfo_transition_latency.attr,
    &scaling_min_freq.attr,
    &scaling_max_freq.attr,
    &affected_cpus.attr,
    --
    1.6.0.2


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