On 06/03/2014 03:38 PM, Viresh Kumar wrote:
> On 3 June 2014 15:34, Srivatsa S. Bhat <[email protected]>
> wrote:
>> Well, the method I used keeps the organization such that the code following
>> the comment does precisely what the comment says (i.e, get the sampling_rate,
>> fetch the multiplier, and then multiply). So I feel it makes it easier to
>> understand.
>
> It looked like the comment is there only for this special statement:
>
>>>> + sampling_rate *= od_dbs_info->rate_mult;
>
> And so suggested that :)
>
> Anyway move this up as it doesn't belong to comment for sure.
>>> + od_dbs_info = dbs_data->cdata->get_cpu_dbs_info_s(cpu);
>
Fair enough :) Here it is:
diff --git a/drivers/cpufreq/cpufreq_governor.c
b/drivers/cpufreq/cpufreq_governor.c
index e1c6433..2597bbe 100644
--- a/drivers/cpufreq/cpufreq_governor.c
+++ b/drivers/cpufreq/cpufreq_governor.c
@@ -36,14 +36,29 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu)
struct od_dbs_tuners *od_tuners = dbs_data->tuners;
struct cs_dbs_tuners *cs_tuners = dbs_data->tuners;
struct cpufreq_policy *policy;
+ unsigned int sampling_rate;
unsigned int max_load = 0;
unsigned int ignore_nice;
unsigned int j;
- if (dbs_data->cdata->governor == GOV_ONDEMAND)
+ if (dbs_data->cdata->governor == GOV_ONDEMAND) {
+ struct od_cpu_dbs_info_s *od_dbs_info =
+ dbs_data->cdata->get_cpu_dbs_info_s(cpu);
+
+ /*
+ * Sometimes, the ondemand governor uses an additional
+ * multiplier to give long delays. So apply this multiplier to
+ * the 'sampling_rate', so as to keep the wake-up-from-idle
+ * detection logic a bit conservative.
+ */
+ sampling_rate = od_tuners->sampling_rate;
+ sampling_rate *= od_dbs_info->rate_mult;
+
ignore_nice = od_tuners->ignore_nice_load;
- else
+ } else {
+ sampling_rate = cs_tuners->sampling_rate;
ignore_nice = cs_tuners->ignore_nice_load;
+ }
policy = cdbs->cur_policy;
@@ -96,7 +111,29 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu)
if (unlikely(!wall_time || wall_time < idle_time))
continue;
- load = 100 * (wall_time - idle_time) / wall_time;
+ /*
+ * If the CPU had gone completely idle, and a task just woke up
+ * on this CPU now, it would be unfair to calculate 'load' the
+ * usual way for this elapsed time-window, because it will show
+ * near-zero load, irrespective of how CPU intensive the new
+ * task is. This is undesirable for latency-sensitive bursty
+ * workloads.
+ *
+ * To avoid this, we reuse the 'load' from the previous
+ * time-window and give this task a chance to start with a
+ * reasonably high CPU frequency.
+ *
+ * Detecting this situation is easy: the governor's deferrable
+ * timer would not have fired during CPU-idle periods. Hence
+ * an unusually large 'wall_time' (as compared to the sampling
+ * rate) indicates this scenario.
+ */
+ if (unlikely(wall_time > (2 * sampling_rate))) {
+ load = j_cdbs->prev_load;
+ } else {
+ load = 100 * (wall_time - idle_time) / wall_time;
+ j_cdbs->prev_load = load;
+ }
if (load > max_load)
max_load = load;
@@ -323,6 +360,10 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy,
j_cdbs->cur_policy = policy;
j_cdbs->prev_cpu_idle = get_cpu_idle_time(j,
&j_cdbs->prev_cpu_wall, io_busy);
+ j_cdbs->prev_load = 100 * (j_cdbs->prev_cpu_wall -
+ j_cdbs->prev_cpu_idle) /
+ j_cdbs->prev_cpu_wall;
+
if (ignore_nice)
j_cdbs->prev_cpu_nice =
kcpustat_cpu(j).cpustat[CPUTIME_NICE];
diff --git a/drivers/cpufreq/cpufreq_governor.h
b/drivers/cpufreq/cpufreq_governor.h
index bfb9ae1..b56552b 100644
--- a/drivers/cpufreq/cpufreq_governor.h
+++ b/drivers/cpufreq/cpufreq_governor.h
@@ -134,6 +134,7 @@ struct cpu_dbs_common_info {
u64 prev_cpu_idle;
u64 prev_cpu_wall;
u64 prev_cpu_nice;
+ unsigned int prev_load;
struct cpufreq_policy *cur_policy;
struct delayed_work work;
/*
--
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