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    Subject[PATCH 8/7] cpufreq: make the iowait-is-busy-time a sysfs tunable
    On Tue, 27 Apr 2010 13:39:34 +0200
    Thomas Renninger <trenn@suse.de> wrote:

    > On Friday 23 April 2010 06:08:19 pm Arjan van de Ven wrote:
    > > On Fri, 23 Apr 2010 10:50:10 +0200
    > > Thomas Renninger <trenn@suse.de> wrote:
    > > Especially on battery, users will appreciate some minutes
    > >
    > > > of more battery lifetime and do not care about some ms of IO
    > > > latencies.
    > >
    > > the assumption that power doesn't matter on AC is a huge fiction
    > > that any data center operator would love to get out of everyones
    > > head as quickly as possible.
    >
    > Have I said power doesn't matter on AC?
    > Do you agree that a datacenter has different performance vs power
    > tradeoff demands as a battery driven mobile device?
    >
    > Back to the topic:
    > As you did not answer on my (several) sysfs knob request(s), I expect
    > you agree with it and will add one.
    >

    yup it makes sense to have a sysfs knob with a sane default value

    From: Arjan van de Ven <arjan@linux.intel.com>
    Subject: [PATCH] cpufreq: make the iowait-is-busy-time a sysfs tunable

    Pavel Machek pointed out that not all CPUs have an efficient idle
    at high frequency. Specifically, older Intel and various AMD cpus
    would get a higher power usage when copying files from USB.

    Mike Chan pointed out that the same is true for various ARM chips
    as well.

    Thomas Renninger suggested to make this a sysfs tunable with a
    reasonable default.

    This patch adds a sysfs tunable for the new behavior, and uses
    a very simple function to determine a reasonable default, depending
    on the CPU vendor/type.

    Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
    ---
    drivers/cpufreq/cpufreq_ondemand.c | 46 +++++++++++++++++++++++++++++++++++-
    1 files changed, 45 insertions(+), 1 deletions(-)

    diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
    index ed472f8..4877e8f 100644
    --- a/drivers/cpufreq/cpufreq_ondemand.c
    +++ b/drivers/cpufreq/cpufreq_ondemand.c
    @@ -109,6 +109,7 @@ static struct dbs_tuners {
    unsigned int down_differential;
    unsigned int ignore_nice;
    unsigned int powersave_bias;
    + unsigned int io_is_busy;
    } dbs_tuners_ins = {
    .up_threshold = DEF_FREQUENCY_UP_THRESHOLD,
    .down_differential = DEF_FREQUENCY_DOWN_DIFFERENTIAL,
    @@ -260,6 +261,7 @@ static ssize_t show_##file_name \
    return sprintf(buf, "%u\n", dbs_tuners_ins.object); \
    }
    show_one(sampling_rate, sampling_rate);
    +show_one(io_is_busy, io_is_busy);
    show_one(up_threshold, up_threshold);
    show_one(ignore_nice_load, ignore_nice);
    show_one(powersave_bias, powersave_bias);
    @@ -310,6 +312,22 @@ static ssize_t store_sampling_rate(struct kobject *a, struct attribute *b,
    return count;
    }

    +static ssize_t store_io_is_busy(struct kobject *a, struct attribute *b,
    + const char *buf, size_t count)
    +{
    + unsigned int input;
    + int ret;
    + ret = sscanf(buf, "%u", &input);
    + if (ret != 1)
    + return -EINVAL;
    +
    + mutex_lock(&dbs_mutex);
    + dbs_tuners_ins.io_is_busy = !!input;
    + mutex_unlock(&dbs_mutex);
    +
    + return count;
    +}
    +
    static ssize_t store_up_threshold(struct kobject *a, struct attribute *b,
    const char *buf, size_t count)
    {
    @@ -392,6 +410,7 @@ static struct global_attr _name = \
    __ATTR(_name, 0644, show_##_name, store_##_name)

    define_one_rw(sampling_rate);
    +define_one_rw(io_is_busy);
    define_one_rw(up_threshold);
    define_one_rw(ignore_nice_load);
    define_one_rw(powersave_bias);
    @@ -403,6 +422,7 @@ static struct attribute *dbs_attributes[] = {
    &up_threshold.attr,
    &ignore_nice_load.attr,
    &powersave_bias.attr,
    + &io_is_busy.attr,
    NULL
    };

    @@ -527,7 +547,7 @@ static void dbs_check_cpu(struct cpu_dbs_info_s *this_dbs_info)
    * from the cpu idle time.
    */

    - if (idle_time >= iowait_time)
    + if (dbs_tuners_ins.io_is_busy && idle_time >= iowait_time)
    idle_time -= iowait_time;

    if (unlikely(!wall_time || wall_time < idle_time))
    @@ -643,6 +663,29 @@ static inline void dbs_timer_exit(struct cpu_dbs_info_s *dbs_info)
    cancel_delayed_work_sync(&dbs_info->work);
    }

    +/*
    + * Not all CPUs want IO time to be accounted as busy; this depends on how
    + * efficient idling at a higher frequency/voltage is.
    + * Pavel Machek says this is not so for various generations of AMD and old
    + * Intel systems.
    + * Mike Chan (android.com) says this is also not true for ARM.
    + * Because of this, whitelist specific known (series) of CPUs by default, and
    + * leave all others up to the user.
    + */
    +static int should_io_be_busy(void)
    +{
    +#if defined(CONFIG_X86)
    + /*
    + * For Intel, Core 2 (model 15) and later have an efficient idle.
    + */
    + if (boot_cpu_data.x86_vendor == X86_VENDOR_INTEL &&
    + boot_cpu_data.x86 == 6 &&
    + boot_cpu_data.x86_model >= 15)
    + return 1;
    +#endif
    + return 0;
    +}
    +
    static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
    unsigned int event)
    {
    @@ -705,6 +748,7 @@ static int cpufreq_governor_dbs(struct cpufreq_policy *policy,
    dbs_tuners_ins.sampling_rate =
    max(min_sampling_rate,
    latency * LATENCY_MULTIPLIER);
    + dbs_tuners_ins.io_is_busy = should_io_be_busy();
    }
    mutex_unlock(&dbs_mutex);

    --
    1.6.1.3



    --
    Arjan van de Ven Intel Open Source Technology Centre
    For development, discussion and tips for power savings,
    visit http://www.lesswatts.org


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