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Date: Tue, 4 May 2010 07:43:32 +0200
From: Pavel Machek <pavel@....cz>
To: Arjan van de Ven <arjan@...radead.org>
Cc: Thomas Renninger <trenn@...e.de>, Willy Tarreau <w@....eu>,
linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
mingo@...e.hu, peterz@...radead.org, tglx@...utronix.de,
davej@...hat.com, cpufreq@...r.kernel.org, riel@...hat.com
Subject: Re: [PATCH 8/7] cpufreq: make the iowait-is-busy-time a sysfs
tunable
On Mon 2010-05-03 20:48:18, Arjan van de Ven wrote:
> On Tue, 27 Apr 2010 13:39:34 +0200
> Thomas Renninger <trenn@...e.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@...e.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@...ux.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@...ux.intel.com>
ACK.
> ---
> 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);
>
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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