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Date: Wed, 4 Feb 2009 11:07:47 +0100
From: Thomas Renninger <trenn@...e.de>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: davej@...emonkey.org.uk, mark.langsdorf@....com,
cpufreq@...r.kernel.org, venkatesh.pallipadi@...el.com,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] CPUFREQ: ondemand/conservative: sanitize sampling_rate restrictions
On Wednesday 04 February 2009 06:07:25 Andrew Morton wrote:
> On Tue, 3 Feb 2009 17:46:42 +0100 Thomas Renninger <trenn@...e.de> wrote:
> > Limit sampling rate to transition_latency * 100 or kernel limits.
> > If sampling_rate is tried to be set too low, set the lowest allowed
> > value.
> >
> > Signed-off-by: Thomas Renninger <trenn@...e.de>
> > ---
> > Documentation/cpu-freq/governors.txt | 14 +++++++++++++-
> > drivers/cpufreq/cpufreq_conservative.c | 19 ++++++++++++++++---
> > drivers/cpufreq/cpufreq_ondemand.c | 19 +++++++++++++++----
> > 3 files changed, 44 insertions(+), 8 deletions(-)
> >
> > diff --git a/Documentation/cpu-freq/governors.txt
> > b/Documentation/cpu-freq/governors.txt index 9b18512..ce73f3e 100644
> > --- a/Documentation/cpu-freq/governors.txt
> > +++ b/Documentation/cpu-freq/governors.txt
> > @@ -117,7 +117,19 @@ accessible parameters:
> > sampling_rate: measured in uS (10^-6 seconds), this is how often you
> > want the kernel to look at the CPU usage and to make decisions on
> > what to do about the frequency. Typically this is set to values of
> > -around '10000' or more.
> > +around '10000' or more. It's default value is (cmp. with
> > users-guide.txt): +transition_latency * 1000
> > +The lowest value you can set is:
> > +transition_latency * 100 or it may get restricted to a value where it
> > +makes not sense for the kernel anymore to poll that often which depends
> > +on your HZ config variable (HZ=1000: max=20000us, HZ=250: max=5000).
> > +Be aware that transition latency is in ns and sampling_rate is in us, so
> > you +get the same sysfs value by default.
> > +Sampling rate should always get adjusted considering the transition
> > latency +To set the sampling rate 750 times as high as the transition
> > latency +in the bash (as said, 1000 is default), do:
> > +echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) \
> > + >ondemand/sampling_rate
> >
> > show_sampling_rate_(min|max): THIS INTERFACE IS DEPRECATED, DON'T USE
> > IT. You can use wider ranges now and the general
> > diff --git a/drivers/cpufreq/cpufreq_conservative.c
> > b/drivers/cpufreq/cpufreq_conservative.c index 5ba0a3f..b8bbd4a 100644
> > --- a/drivers/cpufreq/cpufreq_conservative.c
> > +++ b/drivers/cpufreq/cpufreq_conservative.c
> > @@ -54,7 +54,18 @@ static unsigned int def_sampling_rate;
> > (MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10))
> > #define MIN_SAMPLING_RATE \
> > (def_sampling_rate / MIN_SAMPLING_RATE_RATIO)
This one will vanish after the deprecation time expired.
> > +/* Above MIN_SAMPLING_RATE will vanish with its sysfs file soon
> > + * Define the minimal settable sampling rate to the greater of:
> > + * - "HW transition latency" * 100 (same as default sampling / 10)
> > + * - MIN_STAT_SAMPLING_RATE
> > + * To avoid that userspace shoots itself.
> > +*/
> > +#define MINIMUM_SAMPLING_RATE \
> > + ((def_sampling_rate / 10) < MIN_STAT_SAMPLING_RATE \
> > + ? MIN_STAT_SAMPLING_RATE : (def_sampling_rate / 10))
>
> Use
> max(def_sampling_rate / 10, MIN_STAT_SAMPLING_RATE)
> ?
Ok.
> But really, this should be a plain old C function. Hiding a bunch of C
> code inside a macro which purports to be a compile-time constant is rude.
>
> > +/* This will also vanish soon with removing sampling_rate_max */
> > #define MAX_SAMPLING_RATE (500 * def_sampling_rate)
>
> Ditto, really.
This one will also be removed after the deprecation time expired.
Therefore I'd prefer to not touch it now and leave it as it is,
but I will remove these with finally removing sampling_rate_{min,max}.
I will also use max(..) where suggested and repost the three, modified
patches.
Thanks for your detailed, review. It's appreciated!
Thomas
> > +
> > #define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER (1000)
> > #define DEF_SAMPLING_DOWN_FACTOR (1)
> > #define MAX_SAMPLING_DOWN_FACTOR (10)
> > @@ -197,12 +208,14 @@ static ssize_t store_sampling_rate(struct
> > cpufreq_policy *unused, ret = sscanf (buf, "%u", &input);
> >
> > mutex_lock(&dbs_mutex);
> > - if (ret != 1 || input > MAX_SAMPLING_RATE || input < MIN_SAMPLING_RATE)
> > { + if (ret != 1) {
> > mutex_unlock(&dbs_mutex);
> > return -EINVAL;
> > }
> > -
> > - dbs_tuners_ins.sampling_rate = input;
> > + if (input < MINIMUM_SAMPLING_RATE)
> > + dbs_tuners_ins.sampling_rate = MINIMUM_SAMPLING_RATE;
> > + else
> > + dbs_tuners_ins.sampling_rate = input;
>
> dbs_tuners_ins.sampling_rate = max(MINIMUM_SAMPLING_RATE, input);
>
> > mutex_unlock(&dbs_mutex);
> >
> > return count;
> > diff --git a/drivers/cpufreq/cpufreq_ondemand.c
> > b/drivers/cpufreq/cpufreq_ondemand.c index 4b42e36..70e0841 100644
> > --- a/drivers/cpufreq/cpufreq_ondemand.c
> > +++ b/drivers/cpufreq/cpufreq_ondemand.c
> > @@ -52,6 +52,16 @@ static unsigned int def_sampling_rate;
> > (MIN_SAMPLING_RATE_RATIO * jiffies_to_usecs(10))
> > #define MIN_SAMPLING_RATE \
> > (def_sampling_rate / MIN_SAMPLING_RATE_RATIO)
> > +/* Above MIN_SAMPLING_RATE will vanish with its sysfs file soon
> > + * Define the minimal settable sampling rate to the greater of:
> > + * - "HW transition latency" * 100 (same as default sampling / 10)
> > + * - MIN_STAT_SAMPLING_RATE
> > + * To avoid that userspace shoots itself.
> > +*/
> > +#define MINIMUM_SAMPLING_RATE \
> > + ((def_sampling_rate / 10) < MIN_STAT_SAMPLING_RATE \
> > + ? MIN_STAT_SAMPLING_RATE : (def_sampling_rate / 10))
> > +/* This will also vanish soon with removing sampling_rate_max */
> > #define MAX_SAMPLING_RATE (500 * def_sampling_rate)
> > #define DEF_SAMPLING_RATE_LATENCY_MULTIPLIER (1000)
> > #define TRANSITION_LATENCY_LIMIT (10 * 1000 * 1000)
> > @@ -243,13 +253,14 @@ static ssize_t store_sampling_rate(struct
> > cpufreq_policy *unused, ret = sscanf(buf, "%u", &input);
> >
> > mutex_lock(&dbs_mutex);
> > - if (ret != 1 || input > MAX_SAMPLING_RATE
> > - || input < MIN_SAMPLING_RATE) {
> > + if (ret != 1) {
> > mutex_unlock(&dbs_mutex);
> > return -EINVAL;
> > }
> > -
> > - dbs_tuners_ins.sampling_rate = input;
> > + if (input < MINIMUM_SAMPLING_RATE)
> > + dbs_tuners_ins.sampling_rate = MINIMUM_SAMPLING_RATE;
> > + else
> > + dbs_tuners_ins.sampling_rate = input;
> > mutex_unlock(&dbs_mutex);
>
> etceterata.
> --
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