Messages in this thread | | | Subject | Re: [RFC][PATCH 7/7] cpufreq: intel_pstate: Change P-state selection algorithm for Core | From | Srinivas Pandruvada <> | Date | Mon, 22 Aug 2016 11:53:46 -0700 |
| |
Hi Doug,
I am not able to apply this patch. Can you send as a patch on top of Rafael's RFC 7/7. Since test takes long time, I want to apply correct patch.
Thanks, Srinivas
On Sat, 2016-08-13 at 08:59 -0700, Doug Smythies wrote: > On 2016.08.05 17:02 Rafael J. Wysocki wrote: > > > > > > > > On 2016.08.03 21:19 Doug Smythies wrote: > > > > > > > > On 2016.07.31 16:49 Rafael J. Wysocki wrote: > > > > > > > > The PID-base P-state selection algorithm used by intel_pstate > > > > for > > > > Core processors is based on very weak foundations. > > > ...[cut]... > > > > > > > > > > > +static inline int32_t get_target_pstate_default(struct cpudata > > > > *cpu) > > > > +{ > > > > + struct sample *sample = &cpu->sample; > > > > + int32_t busy_frac; > > > > + int pstate; > > > > + > > > > + busy_frac = div_fp(sample->mperf, sample->tsc); > > > > + sample->busy_scaled = busy_frac * 100; > > > > + > > > > + if (busy_frac < cpu->iowait_boost) > > > > + busy_frac = cpu->iowait_boost; > > > > + > > > > + cpu->iowait_boost >>= 1; > > > > + > > > > + pstate = cpu->pstate.turbo_pstate; > > > > + return fp_toint((pstate + (pstate >> 2)) * busy_frac); > > > > +} > > > > + > My previous replies (and see below) have suggested that some > filtering > is needed on the target pstate, otherwise, and dependant on the type > of > workload, it tends to oscillate. > > I added the IIR (Infinite Impulse Response) filter that I have > suggested in the past: > > diff --git a/drivers/cpufreq/intel_pstate.c > b/drivers/cpufreq/intel_pstate.c > index c43ef55..262ec5f 100644 > --- a/drivers/cpufreq/intel_pstate.c > +++ b/drivers/cpufreq/intel_pstate.c > @@ -98,6 +98,7 @@ static inline u64 div_ext_fp(u64 x, u64 y) > * @tsc: Difference of time stamp counter between last > and > * current sample > * @time: Current time from scheduler > + * @target: target pstate filtered. > * > * This structure is used in the cpudata structure to store > performance sample > * data for choosing next P State. > @@ -108,6 +109,7 @@ struct sample { > u64 aperf; > u64 mperf; > u64 tsc; > + u64 target; > u64 time; > }; > > @@ -1168,6 +1170,7 @@ static void intel_pstate_get_cpu_pstates(struct > cpudata *cpu) > pstate_funcs.get_vid(cpu); > > intel_pstate_set_min_pstate(cpu); > + cpu->sample.target = int_tofp(cpu->pstate.min_pstate); > } > > static inline void intel_pstate_calc_avg_perf(struct cpudata *cpu) > @@ -1301,8 +1304,10 @@ static inline int32_t > get_target_pstate_use_performance(struct cpudata *cpu) > static inline int32_t get_target_pstate_default(struct cpudata *cpu) > { > struct sample *sample = &cpu->sample; > + int64_t scaled_gain, unfiltered_target; > int32_t busy_frac; > int pstate; > + u64 duration_ns; > > busy_frac = div_fp(sample->mperf, sample->tsc); > sample->busy_scaled = busy_frac * 100; > @@ -1313,7 +1318,74 @@ static inline int32_t > get_target_pstate_default(struct cpudata *cpu) > cpu->iowait_boost >>= 1; > > pstate = cpu->pstate.turbo_pstate; > - return fp_toint((pstate + (pstate >> 2)) * busy_frac); > + /* To Do: I think the above should be: > + * > + * if (limits.no_turbo || limits.turbo_disabled) > + * pstate = cpu->pstate.max_pstate; > + * else > + * pstate = cpu->pstate.turbo_pstate; > + * > + * figure it out. > + * > + * no clamps. Pre-filter clamping was needed in past > implementations. > + * To Do: Is any pre-filter clamping needed here? */ > + > + unfiltered_target = (pstate + (pstate >> 2)) * busy_frac; > + > + /* > + * Idle check. > + * We have a deferrable timer. Very long durations can be > + * either due to long idle (C0 time near 0), > + * or due to short idle times that spanned jiffy boundaries > + * (C0 time not near zero). > + * > + * To Do: As of the utilization stuff, I do not think the > + * spanning jiffy boundaries thing is true anymore. > + * Check, and fix the comment. > + * > + * The very long durations are 0.4 seconds or more. > + * Either way, a very long duration will effectively flush > + * the IIR filter, otherwise falling edge load response times > + * can be on the order of tens of seconds, because this > driver > + * runs very rarely. Furthermore, for higher periodic loads > that > + * just so happen to not be in the C0 state on jiffy > boundaries, > + * the long ago history should be forgotten. > + * For cases of durations that are a few times the set sample > + * period, increase the IIR filter gain so as to weight > + * the current sample more appropriately. > + * > + * To Do: sample_time should be forced to be accurate. For > + * example if the kernel is a 250 Hz kernel, then a > + * sample_rate_ms of 10 should result in a sample_time of 12. > + * > + * To Do: Check that the IO Boost case is not filtered too > much. > + * It might be that a filter by-pass is needed for the > boost case. > + * However, the existing gain = f(duration) might be > good enough. > + */ > + > + duration_ns = cpu->sample.time - cpu->last_sample_time; > + > + scaled_gain = div_u64(int_tofp(duration_ns) * > + int_tofp(pid_params.p_gain_pct), > int_tofp(pid_params.sample_rate_ns)); > + if (scaled_gain > int_tofp(100)) > + scaled_gain = int_tofp(100); > + /* > + * This code should not be required, > + * but short duration times have been observed > + * To Do: Check if this code is actually still needed. I > don't think so. > + */ > + if (scaled_gain < int_tofp(pid_params.p_gain_pct)) > + scaled_gain = int_tofp(pid_params.p_gain_pct); > + > + /* > + * Bandwidth limit the output. For now, re-task p_gain_pct > for this purpose. > + * Use a smple IIR (Infinite Impulse Response) filter. > + */ > + cpu->sample.target = div_u64((int_tofp(100) - scaled_gain) * > + cpu->sample.target + scaled_gain * > + unfiltered_target, int_tofp(100)); > + > + return fp_toint(cpu->sample.target + (1 << (FRAC_BITS-1))); > } > > static inline void intel_pstate_update_pstate(struct cpudata *cpu, > int pstate) > @@ -1579,6 +1651,7 @@ static void intel_pstate_stop_cpu(struct > cpufreq_policy *policy) > return; > > intel_pstate_set_min_pstate(cpu); > + cpu->sample.target = int_tofp(cpu->pstate.min_pstate); > } > > static int intel_pstate_cpu_init(struct cpufreq_policy *policy) > > The filter introduces a trade-off between step function load response > time > and the tendency for the target pstate to oscillate. > > ...[cut]... > > > > > > > > > Several tests were done with this patch set. > > > The patch set would not apply to kernel 4.7, but did apply fine > > > to a 4.7+ kernel > > > (I did as of 7a66ecf) from a few days ago. > > > > > > Test 1: Phoronix ffmpeg test (less time is better): > > > Reason: Because it suffers from rotating amongst CPUs in an odd > > > way, challenging for CPU frequency scaling drivers. > > > This test tends to be an indicator of potential troubles with > > > some games. > > > Criteria: (Dirk Brandewie): Must match or better acpi_cpufreq - > > > ondemand. > > > With patch set: 15.8 Seconds average and 24.51 package watts. > > > Without patch set: 11.61 Seconds average and 27.59 watts. > > > Conclusion: Significant reduction in performance with proposed > > > patch set. > With the filter this become even worse at ~18 seconds. > I used to fix this by moving the response curve to the left. > I have not tested this: > > + unfiltered_target = (pstate + (pstate >> 1)) * busy_frac; > > which moves the response curve left a little, yet. I will test it. > > ...[cut]... > > > > > > > > > Test 9: Doug's_specpower simulator (20% load): > > > Time is fixed, less energy is better. > > > Reason: During the long > > > "[intel-pstate driver regression] processor frequency very high > > > even if in idle" > > > and subsequent https://bugzilla.kernel.org/show_bug.cgi?id=115771 > > > discussion / thread(s), some sort of test was needed to try to > > > mimic what Srinivas > > > was getting on his fancy SpecPower test platform. So far at > > > least, this test does that. > > > Only the 20% load case was created, because that was the biggest > > > problem case back then. > > > With patch set: 4 tests at an average of 7197 Joules per test, > > > relatively high CPU frequencies. > > > Without the patch set: 4 tests at an average of 5956 Joules per > > > test, relatively low CPU frequencies. > > > Conclusion: 21% energy regression with the patch set. > > > Note: Newer processors might do better than my older i7-2600K. > Patch set + above and IIR gain = 10%: 5670 Joules. > Conclusion: Energy regression eliminated. > > Other gains: > > gain = 5%: 5342 Joules; Busy MHz: 2172 > gain = 10%: 5670 Joules; Busy MHz: 2285 > gain = 20%: 6126 Joules; Busy MHz: 2560 > gain = 30%: 6426 Joules; Busy MHz: 2739 > gain = 40%: 6674 Joules; Busy MHz: 2912 > gain = 70%: 7109 Joules; Busy MHz: 3199 > > locked at minimum pstate (reference): 4653 Joules; Busy MHz: 1600 > Performance mode (reference): 7808 Joules; Busy MHz: 3647 > > > > > > > > > Test 10: measure the frequency response curve, fixed work packet > > > method, > > > 75 hertz work / sleep frequency (all CPU, no IOWAIT): > > > Reason: To compare to some older data and observe overall. > > > png graph NOT attached. > > > Conclusions: Tends to oscillate, suggesting some sort of damping > > > is needed. > > > However, any filtering tends to increase the step function load > > > rise time > > > (see test 11 below, I think there is some wiggle room here). > > > See also graph which has: with and without patch set; performance > > > mode (for reference); > > > Philippe Longepe's cpu_load method also with setpoint 40 (for > > > reference); one of my previous > > > attempts at a load related patch set from quite some time ago > > > (for reference). > As expected, the filter damps out the oscillation. > New graphs will be sent to Rafael and Srinivas off-list. > > > > > > > > > > > > Test 11: Look at the step function load response. From no load to > > > 100% on one CPU (CPU load only, no IO). > > > While there is a graph, it is not attached: > > > Conclusion: The step function response is greatly improved > > > (virtually one sample time max). > > > It would probably be O.K. to slow it down a little with a filter > > > so as to reduce the > > > tendency to oscillate under periodic load conditions (to a point, > > > at least. A low enough frequency will > > > always oscillate) (see the graph for test10). > I haven't done this test yet, but from previous work, a gain setting > of 10 to 15% gives a > load step function response time similar to the current PID based > filter. > > The other tests gave similar results with or without the filter. > > ... Doug > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-pm" > in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
| |