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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2016-04-02 01:06:21 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2016-04-02 01:06:21 +0200
commitfebce40febcff3ccdb33f63456ffc4cfc61640c8 (patch)
treee631d4e2aa9251c36d63ff40c4fbb1ad02d005ae /drivers/cpufreq
parentbb6ab52f2befe1fb29ac198f27d8a6aadf510f81 (diff)
downloadlinux-febce40febcff3ccdb33f63456ffc4cfc61640c8.tar.bz2
intel_pstate: Avoid extra invocation of intel_pstate_sample()
The initialization of intel_pstate for a given CPU involves populating the fields of its struct cpudata that represent the previous sample, but currently that is done in a problematic way. Namely, intel_pstate_init_cpu() makes an extra call to intel_pstate_sample() so it reads the current register values that will be used to populate the "previous sample" record during the next invocation of intel_pstate_sample(). However, after commit a4675fbc4a7a (cpufreq: intel_pstate: Replace timers with utilization update callbacks) that doesn't work for last_sample_time, because the time value is passed to intel_pstate_sample() as an argument now. Passing 0 to it from intel_pstate_init_cpu() is problematic, because that causes cpu->last_sample_time == 0 to be visible in get_target_pstate_use_performance() (and hence the extra cpu->last_sample_time > 0 check in there) and effectively allows the first invocation of intel_pstate_sample() from intel_pstate_update_util() to happen immediately after the initialization which may lead to a significant "turn on" effect in the governor algorithm. To mitigate that issue, rework the initialization to avoid the extra intel_pstate_sample() call from intel_pstate_init_cpu(). Instead, make intel_pstate_sample() return false if it has been called with cpu->sample.time equal to zero, which will make intel_pstate_update_util() skip the sample in that case, and reset cpu->sample.time from intel_pstate_set_update_util_hook() to make the algorithm start properly every time the hook is set. Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/cpufreq')
-rw-r--r--drivers/cpufreq/intel_pstate.c21
1 files changed, 15 insertions, 6 deletions
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 81057e48c4de..9ae159631f52 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -910,7 +910,14 @@ static inline bool intel_pstate_sample(struct cpudata *cpu, u64 time)
cpu->prev_aperf = aperf;
cpu->prev_mperf = mperf;
cpu->prev_tsc = tsc;
- return true;
+ /*
+ * First time this function is invoked in a given cycle, all of the
+ * previous sample data fields are equal to zero or stale and they must
+ * be populated with meaningful numbers for things to work, so assume
+ * that sample.time will always be reset before setting the utilization
+ * update hook and make the caller skip the sample then.
+ */
+ return !!cpu->last_sample_time;
}
static inline int32_t get_avg_frequency(struct cpudata *cpu)
@@ -984,8 +991,7 @@ static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
* enough period of time to adjust our busyness.
*/
duration_ns = cpu->sample.time - cpu->last_sample_time;
- if ((s64)duration_ns > pid_params.sample_rate_ns * 3
- && cpu->last_sample_time > 0) {
+ if ((s64)duration_ns > pid_params.sample_rate_ns * 3) {
sample_ratio = div_fp(int_tofp(pid_params.sample_rate_ns),
int_tofp(duration_ns));
core_busy = mul_fp(core_busy, sample_ratio);
@@ -1100,7 +1106,6 @@ static int intel_pstate_init_cpu(unsigned int cpunum)
intel_pstate_get_cpu_pstates(cpu);
intel_pstate_busy_pid_reset(cpu);
- intel_pstate_sample(cpu, 0);
cpu->update_util.func = intel_pstate_update_util;
@@ -1121,9 +1126,13 @@ static unsigned int intel_pstate_get(unsigned int cpu_num)
return get_avg_frequency(cpu);
}
-static void intel_pstate_set_update_util_hook(unsigned int cpu)
+static void intel_pstate_set_update_util_hook(unsigned int cpu_num)
{
- cpufreq_set_update_util_data(cpu, &all_cpu_data[cpu]->update_util);
+ struct cpudata *cpu = all_cpu_data[cpu_num];
+
+ /* Prevent intel_pstate_update_util() from using stale data. */
+ cpu->sample.time = 0;
+ cpufreq_set_update_util_data(cpu_num, &cpu->update_util);
}
static void intel_pstate_clear_update_util_hook(unsigned int cpu)