intel_pstate: Fix intel_pstate_get()

rafaeljw · rafaeljw · commit 6d45b719cbd5 · 2016-05-04T14:09:16.000+02:00
After commit 8fa520a "intel_pstate: Remove freq calculation from intel_pstate_calc_busy()" intel_pstate_get() calls get_avg_frequency() to compute the average frequency, which is problematic for two reasons. First, intel_pstate_get() may be invoked before the driver reads the CPU feedback registers for the first time and if that happens, get_avg_frequency() will attempt to divide by zero. Second, the get_avg_frequency() call in intel_pstate_get() is racy with respect to intel_pstate_sample() and it may end up returning completely meaningless values for this reason. Moreover, after commit 7349ec0 "intel_pstate: Move intel_pstate_calc_busy() into get_target_pstate_use_performance()" sample.core_pct_busy is never computed on Atom, but it is used in intel_pstate_adjust_busy_pstate() in that case too. To address those problems notice that if sample.core_pct_busy was used in the average frequency computation carried out by get_avg_frequency(), both the divide by zero problem and the race with respect to intel_pstate_sample() would be avoided. Accordingly, move the invocation of intel_pstate_calc_busy() from get_target_pstate_use_performance() to intel_pstate_update_util(), which also will take care of the uninitialized sample.core_pct_busy on Atom, and modify get_avg_frequency() to use sample.core_pct_busy as per the above. Reported-by: kernel test robot <ying.huang@linux.intel.com> Link: http://marc.info/?l=linux-kernel&m=146226437623173&w=4 Fixes: 8fa520a "intel_pstate: Remove freq calculation from intel_pstate_calc_busy()" Fixes: 7349ec0 "intel_pstate: Move intel_pstate_calc_busy() into get_target_pstate_use_performance()" Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c
@@ -1070,8 +1070,9 @@ static inline bool intel_pstate_sample(struct cpudata *cpu, u64 time)
 
 static inline int32_t get_avg_frequency(struct cpudata *cpu)
 {
-	return div64_u64(cpu->pstate.max_pstate_physical * cpu->sample.aperf *
-		cpu->pstate.scaling, cpu->sample.mperf);
+	return fp_toint(mul_fp(cpu->sample.core_pct_busy,
+			       int_tofp(cpu->pstate.max_pstate_physical *
+						cpu->pstate.scaling / 100)));
 }
 
 static inline int32_t get_target_pstate_use_cpu_load(struct cpudata *cpu)
@@ -1114,8 +1115,6 @@ static inline int32_t get_target_pstate_use_performance(struct cpudata *cpu)
 	int32_t core_busy, max_pstate, current_pstate, sample_ratio;
 	u64 duration_ns;
 
-	intel_pstate_calc_busy(cpu);
-
 	/*
 	 * core_busy is the ratio of actual performance to max
 	 * max_pstate is the max non turbo pstate available
@@ -1199,8 +1198,11 @@ static void intel_pstate_update_util(struct update_util_data *data, u64 time,
 	if ((s64)delta_ns >= pid_params.sample_rate_ns) {
 		bool sample_taken = intel_pstate_sample(cpu, time);
 
-		if (sample_taken && !hwp_active)
-			intel_pstate_adjust_busy_pstate(cpu);
+		if (sample_taken) {
+			intel_pstate_calc_busy(cpu);
+			if (!hwp_active)
+				intel_pstate_adjust_busy_pstate(cpu);
+		}
 	}
 }
 
