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    SubjectRe: [RFC PATCH 2/2] CPUfreq ondemand: handle QoS request on DVFS response latency
    Date
    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@samsung.com>
    > > Signed-off-by: Kyungmin Park <kyungmin.park@samsung.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


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