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authorRafael J. Wysocki <rafael.j.wysocki@intel.com>2016-04-10 05:59:10 +0200
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2016-04-10 05:59:10 +0200
commitffb810563c0c049872a504978e06c8892104fb6c (patch)
tree5f85788101c16dd3c06f420a0809a75eef0db2d7 /drivers/cpufreq/intel_pstate.c
parentb318556479cc923970a79d6c2311138581c0db83 (diff)
downloadop-kernel-dev-ffb810563c0c049872a504978e06c8892104fb6c.zip
op-kernel-dev-ffb810563c0c049872a504978e06c8892104fb6c.tar.gz
intel_pstate: Avoid getting stuck in high P-states when idle
Jörg Otte reports that commit a4675fbc4a7a (cpufreq: intel_pstate: Replace timers with utilization update callbacks) caused the CPUs in his Haswell-based system to stay in the very high frequency region even if the system is completely idle. That turns out to be an existing problem in the intel_pstate driver's P-state selection algorithm for Core processors. Namely, all decisions made by that algorithm are based on the average frequency of the CPU between sampling events and on the P-state requested on the last invocation, so it may get stuck at a very hight frequency even if the utilization of the CPU is very low (in fact, it may get stuck in a inadequate P-state regardless of the CPU utilization). The only way to kick it out of that limbo is a sufficiently long idle period (3 times longer than the prescribed sampling interval), but if that doesn't happen often enough (eg. due to a timing change like after the above commit), the P-state of the CPU may be inadequate pretty much all the time. To address the most egregious manifestations of that issue, reset the core_busy value used to determine the next P-state to request if the utilization of the CPU, determined with the help of the MPERF feedback register and the TSC, is below 1%. Link: https://bugzilla.kernel.org/show_bug.cgi?id=115771 Reported-and-tested-by: Jörg Otte <jrg.otte@gmail.com> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Diffstat (limited to 'drivers/cpufreq/intel_pstate.c')
-rw-r--r--drivers/cpufreq/intel_pstate.c4
1 files changed, 4 insertions, 0 deletions
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
index 8b5a415..30fe323 100644
--- a/drivers/cpufreq/intel_pstate.c
+++ b/drivers/cpufreq/intel_pstate.c
@@ -1130,6 +1130,10 @@ static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
sample_ratio = div_fp(int_tofp(pid_params.sample_rate_ns),
int_tofp(duration_ns));
core_busy = mul_fp(core_busy, sample_ratio);
+ } else {
+ sample_ratio = div_fp(100 * cpu->sample.mperf, cpu->sample.tsc);
+ if (sample_ratio < int_tofp(1))
+ core_busy = 0;
}
cpu->sample.busy_scaled = core_busy;
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