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Message-ID: <CAJ0PZbTP5t9krrPi83EP5qziWbLkW4GtJpMQKM2OznzzNZd3GQ@mail.gmail.com>
Date: Tue, 28 Feb 2012 09:39:17 +0900
From: MyungJoo Ham <myungjoo.ham@...il.com>
To: "Rafael J. Wysocki" <rjw@...k.pl>
Cc: Pavel Machek <pavel@....cz>, cpufreq@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
Dave Jones <davej@...hat.com>, Len Brown <len.brown@...el.com>,
Kevin Hilman <khilman@...com>, Jean Pihet <j-pihet@...com>,
markgross <markgross@...gnar.org>, kyungmin.park@...sung.com
Subject: Re: [RFC PATCH 2/2] CPUfreq ondemand: handle QoS request on DVFS
response latency
On Sun, Feb 26, 2012 at 8:47 AM, Rafael J. Wysocki <rjw@...k.pl> wrote:
> On Saturday, February 25, 2012, Pavel Machek wrote:
>> On Wed 2012-02-22 17:03:35, MyungJoo Ham wrote:
>> > With QoS class, DVFS_RESPONSE_LATENCY, users (device drivers and
>> > userspace processes) may express the desired maximum response latency
>> > from DVFS mechanisms such as CPUfreq's ondemand governors. Based on such
>> > QoS requests, the ondemand governor may flexibly adjust sampling rate
>> > accordingly unless it goes below the min_sampling_rate.
>> >
>> > The benefit of having DVFS_RESPONSE_LATENCY is to have faster response
>> > from user inputs (mouse clicks, keyboard inputs, touchscreen touches,
>> > and others) without increasing frequency unconditionally. Because some
>> > input events may not require any performance increases, increasing the
>> > frequency unconditionally for inputs may simply consume too much energy.
>> > Adjusting sampling rate based on user inputs enabled to increase
>> > frequency with less latency if it requires and not to increase frequency
>> > if it does not require.
>> >
>> > Signed-off-by: MyungJoo Ham <myungjoo.ham@...sung.com>
>> > Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
>> >
>> > --
>> > This patch depends on the patch
>> > "PM / QoS: Introduce new classes: DMA-Throughput and DVFS-Latency".
>> > and the patch
>> > "CPUfreq ondemand: update sampling rate without waiting for next
>> > sampling"
>> > ---
>> > drivers/cpufreq/cpufreq_ondemand.c | 108 ++++++++++++++++++++++++++++++++----
>> > 1 files changed, 96 insertions(+), 12 deletions(-)
>> >
>> > diff --git a/drivers/cpufreq/cpufreq_ondemand.c b/drivers/cpufreq/cpufreq_ondemand.c
>> > index 2d66649..b9188f1 100644
>> > --- a/drivers/cpufreq/cpufreq_ondemand.c
>> > +++ b/drivers/cpufreq/cpufreq_ondemand.c
>> > @@ -22,6 +22,7 @@
>> > #include <linux/tick.h>
>> > #include <linux/ktime.h>
>> > #include <linux/sched.h>
>> > +#include <linux/pm_qos.h>
>> >
>> > /*
>> > * dbs is used in this file as a shortform for demandbased switching
>> > @@ -93,6 +94,7 @@ struct cpu_dbs_info_s {
>> > * when user is changing the governor or limits.
>> > */
>> > struct mutex timer_mutex;
>> > + bool activated; /* dbs_timer_init is in effect */
>> > };
>> > static DEFINE_PER_CPU(struct cpu_dbs_info_s, od_cpu_dbs_info);
>> >
>> > @@ -111,6 +113,8 @@ static struct dbs_tuners {
>> > unsigned int sampling_down_factor;
>> > unsigned int powersave_bias;
>> > unsigned int io_is_busy;
>> > + struct notifier_block dvfs_lat_qos_db;
>> > + unsigned int dvfs_lat_qos_wants;
>> > } dbs_tuners_ins = {
>> > .up_threshold = DEF_FREQUENCY_UP_THRESHOLD,
>> > .sampling_down_factor = DEF_SAMPLING_DOWN_FACTOR,
>> > @@ -164,6 +168,23 @@ static inline cputime64_t get_cpu_iowait_time(unsigned int cpu, cputime64_t *wal
>> > }
>> >
>> > /*
>> > + * Find right sampling rate based on sampling_rate and
>> > + * QoS requests on dvfs latency.
>> > + */
>> > +static unsigned int effective_sampling_rate(void)
>> > +{
>> > + unsigned int effective;
>> > +
>> > + if (dbs_tuners_ins.dvfs_lat_qos_wants)
>> > + effective = min(dbs_tuners_ins.dvfs_lat_qos_wants,
>> > + dbs_tuners_ins.sampling_rate);
>> > + else
>> > + effective = dbs_tuners_ins.sampling_rate;
>> > +
>> > + return max(effective, min_sampling_rate);
>> > +}
>> > +
>> > +/*
>> > * Find right freq to be set now with powersave_bias on.
>> > * Returns the freq_hi to be used right now and will set freq_hi_jiffies,
>> > * freq_lo, and freq_lo_jiffies in percpu area for averaging freqs.
>> > @@ -207,7 +228,7 @@ static unsigned int powersave_bias_target(struct cpufreq_policy *policy,
>> > dbs_info->freq_lo_jiffies = 0;
>> > return freq_lo;
>> > }
>> > - jiffies_total = usecs_to_jiffies(dbs_tuners_ins.sampling_rate);
>> > + jiffies_total = usecs_to_jiffies(effective_sampling_rate());
>> > jiffies_hi = (freq_avg - freq_lo) * jiffies_total;
>> > jiffies_hi += ((freq_hi - freq_lo) / 2);
>> > jiffies_hi /= (freq_hi - freq_lo);
>> > @@ -259,7 +280,8 @@ show_one(powersave_bias, powersave_bias);
>> >
>> > /**
>> > * update_sampling_rate - update sampling rate effective immediately if needed.
>> > - * @new_rate: new sampling rate
>> > + * @new_rate: new sampling rate. if it is 0, regard sampling rate is not
>> > + * changed and assume that qos request value is changed.
>> > *
>> > * If new rate is smaller than the old, simply updaing
>> > * dbs_tuners_int.sampling_rate might not be appropriate. For example,
>> > @@ -273,9 +295,13 @@ show_one(powersave_bias, powersave_bias);
>> > static void update_sampling_rate(unsigned int new_rate)
>> > {
>> > int cpu;
>> > + unsigned int effective;
>> > +
>> > +
>> > + if (new_rate)
>> > + dbs_tuners_ins.sampling_rate = max(new_rate, min_sampling_rate);
>> >
>> > - dbs_tuners_ins.sampling_rate = new_rate
>> > - = max(new_rate, min_sampling_rate);
>> > + effective = effective_sampling_rate();
>> >
>> > for_each_online_cpu(cpu) {
>> > struct cpufreq_policy *policy;
>> > @@ -283,21 +309,31 @@ static void update_sampling_rate(unsigned int new_rate)
>> > struct timer_list *timer;
>> > unsigned long appointed_at;
>> >
>> > + /*
>> > + * mutex_destory(&dbs_info->timer_mutex) should not happen
>> > + * in this context.
>> > + */
>> > + mutex_lock(&dbs_mutex);
>> > +
>> > policy = cpufreq_cpu_get(cpu);
>> > if (!policy)
>> > - continue;
>> > + goto next;
>> > dbs_info = &per_cpu(od_cpu_dbs_info, policy->cpu);
>> > cpufreq_cpu_put(policy);
>> >
>> > + /* timer_mutex destroyed or will be destoyed soon */
>> > + if (!dbs_info->activated)
>> > + goto next;
>> > +
>> > mutex_lock(&dbs_info->timer_mutex);
>> >
>> > if (!delayed_work_pending(&dbs_info->work))
>> > - goto next;
>> > + goto next_timer_mutex;
>> >
>> > timer = &dbs_info->work.timer;
>> > appointed_at = timer->expires;
>> >
>> > - if (time_before(jiffies + usecs_to_jiffies(new_rate),
>> > + if (time_before(jiffies + usecs_to_jiffies(effective),
>> > appointed_at)) {
>> >
>> > mutex_unlock(&dbs_info->timer_mutex);
>> > @@ -305,12 +341,15 @@ static void update_sampling_rate(unsigned int new_rate)
>> > mutex_lock(&dbs_info->timer_mutex);
>> >
>> > schedule_delayed_work_on(dbs_info->cpu, &dbs_info->work,
>> > - usecs_to_jiffies(new_rate));
>> > + usecs_to_jiffies(effective));
>> >
>> > }
>> > -next:
>> > +next_timer_mutex:
>> > mutex_unlock(&dbs_info->timer_mutex);
>> > +next:
>> > + mutex_unlock(&dbs_mutex);
>> > }
>> > +
>> > }
>>
>> I don't think gotos are helpful here. Can you use normal program
>> structure or move it to subroutine...?
>
> I agree with Pavel that gotos don't make that code particularly clear.
>
> Thanks,
> Rafael
Ok, I'll let it use a normal if/then/else structure there.
Thanks.
Cheers!
MyungJoo.
--
MyungJoo Ham, Ph.D.
System S/W Lab, S/W Center, Samsung Electronics
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