From: Rafael J. Wysocki <rafael.j.wyso...@intel.com> After commit 8fa520af5081 "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 7349ec0470b6 "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.hu...@linux.intel.com> Link: http://marc.info/?l=linux-kernel&m=146226437623173&w=4 Fixes: 8fa520af5081 "intel_pstate: Remove freq calculation from intel_pstate_calc_busy()" Fixes: 7349ec0470b6 "intel_pstate: Move intel_pstate_calc_busy() into get_target_pstate_use_performance()" Signed-off-by: Rafael J. Wysocki <rafael.j.wyso...@intel.com> --- drivers/cpufreq/intel_pstate.c | 14 ++++++++------ 1 file changed, 8 insertions(+), 6 deletions(-) Index: linux-pm/drivers/cpufreq/intel_pstate.c =================================================================== --- linux-pm.orig/drivers/cpufreq/intel_pstate.c +++ linux-pm/drivers/cpufreq/intel_pstate.c @@ -928,8 +928,9 @@ static inline bool intel_pstate_sample(s 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) @@ -972,8 +973,6 @@ static inline int32_t get_target_pstate_ 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 @@ -1056,8 +1055,11 @@ static void intel_pstate_update_util(str 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); + } } }
