Hi, Doug, Sorry for my late response, and thanks for your information: > -----Original Message----- > From: Doug Smythies [mailto:[email protected]] > Sent: Sunday, October 11, 2015 11:47 PM > To: Chen, Yu C > Cc: Wysocki, Rafael J; [email protected]; [email protected]; [email protected]; > Zhang, Rui; [email protected]; [email protected]; linux- > [email protected]; Brown, Len; 'Ingo Molnar'; 'Pavel Machek'; 'Kristen > Carlson Accardi'; Doug Smythies > Subject: RE: [PATCH] [v4] x86, suspend: Save/restore extra MSR registers for > suspend > > Hi Yu, thanks for your reply. > > On 2015.10.10 19:27 Chen, Yu C wrote: > > On 2105.10.10 02:56 Doug Smythies wrote: > > > >>> The current version of the intel_pstate driver is incompatible with > >>> any use of Clock Modulation, always resulting in driving the target > >>> pstate to the minimum, regardless of load. The result is the > >>> apparent CPU frequency stuck at minimum * modulation percent. > >> > >>> The acpi-cpufreq driver works fine with Clock Modulation, resulting > >>> in desired frequency * modulation percent. > >> > > > [Yu] Why intel_pstate driver is incompatible with Clock Modulation? > > It is simply how the current control algorithm responds to the scenario. > > The problem is in intel_pstate_get_scaled_busy, here: > > /* > * core_busy is the ratio of actual performance to max > * max_pstate is the max non turbo pstate available > * current_pstate was the pstate that was requested during > * the last sample period. > * > * We normalize core_busy, which was our actual percent > * performance to what we requested during the last sample > * period. The result will be a percentage of busy at a > * specified pstate. > */ > core_busy = cpu->sample.core_pct_busy; > max_pstate = int_tofp(cpu->pstate.max_pstate); > current_pstate = int_tofp(cpu->pstate.current_pstate); > core_busy = mul_fp(core_busy, div_fp(max_pstate, current_pstate)); > > With Clock Modulation enabled, the actual performance percent will always > be less than what was asked for, basically meaning current_pstate is much > less than what was asked for. Thus the algorithm will drive down the target > pstate regardless of load. > [Yu] Do you mean, there is some problem with the normalization,and we should use the actual pstate rather than the theoretical current_pstate, for example, the pseudocode might looked like:
- current_pstate = int_tofp(cpu->pstate.current_pstate); + current_pstate = int_tofp(cpu->pstate.current_pstat)*0.85; Best Regards, Yu -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
