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[173.180.45.4]) by smtp.gmail.com with ESMTPSA id d185sm23928770pfd.80.2016.08.25.20.09.59 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 25 Aug 2016 20:10:00 -0700 (PDT) From: Doug Smythies X-Google-Original-From: Doug Smythies To: srinivas.pandruvada@linux.intel.com Cc: rjw@rjwysocki.net, linux-pm@vger.kernel.org, Doug Smythies Subject: [RFC][PATCH 8 of 7 V2] cpufreq: intel_pstate: add iir filter to pstate. Date: Thu, 25 Aug 2016 20:09:41 -0700 Message-Id: <1472180981-29293-1-git-send-email-dsmythies@telus.net> X-Mailer: git-send-email 2.7.4 Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP This is an 8th patch, for on top of Rafael's 7 patch set. See also: http://marc.info/?l=linux-pm&m=147000847031383&w=2 Note: This is not a formal version of this patch, but rather an interim test version. As a function of load / sleep frequency and how it beats against this drivers sampling times, the driver has a tendency to be underdamped and to oscillate, requiring a bandwidth limiting filter on the target PState. Add a simple IIR (Infinite Impulse Response) type filter to the target PState. The purpose is to dampen the inherent oscillations caused by a sampled system that can have measured load extremes in any given sample. The /sys/kernel/debug/pstate_snb/p_gain_pct has been temporarily re-tasked to be the gain for this filter. Optimal nominal gain setting is a tradeoff between response time and adequate damping. Since the time between runs of this driver are so extreme, the gain is adjusted as a function of the time since the last pass so as to reduce, or even eliminate, the influence of what might be a very stale old value. The default gain is 10 percent. V2: Adds clamping of the filtered target pstate Signed-off-by: Doug Smythies --- drivers/cpufreq/intel_pstate.c | 82 ++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 80 insertions(+), 2 deletions(-) diff --git a/drivers/cpufreq/intel_pstate.c b/drivers/cpufreq/intel_pstate.c index c43ef55..752d45c 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; }; @@ -1021,7 +1023,7 @@ static struct cpu_defaults core_params = { .sample_rate_ms = 10, .deadband = 0, .setpoint = 97, - .p_gain_pct = 20, + .p_gain_pct = 10, .d_gain_pct = 0, .i_gain_pct = 0, .boost_iowait = true, @@ -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 +1304,11 @@ 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; + int max_perf, min_perf; + u64 duration_ns; busy_frac = div_fp(sample->mperf, sample->tsc); sample->busy_scaled = busy_frac * 100; @@ -1313,7 +1319,78 @@ 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. + * + */ + + unfiltered_target = (pstate + (pstate >> 2)) * busy_frac; + + /* + * Idle check. + * We have a deferrable timer. Very long durations + * are an indication of idle time since the last pass. + * 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. + * 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: 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. + * + * Bandwidth limit the output. For now, re-task p_gain_pct + * for this purpose. + * Use a smple IIR (Infinite Impulse Response) filter. + * + * Scale the gain as a function of the time since the last run + * of this driver. For example, if the time since the last run + * is 5 times nominal, then the scaled gain is 5 times nominal. + * scaled_gain = gain * duration / nominal + */ + + duration_ns = cpu->sample.time - cpu->last_sample_time; + + scaled_gain = div_u64(int_tofp(duration_ns) * + (pid_params.p_gain_pct), (pid_params.sample_rate_ns)); + if (scaled_gain > int_tofp(100)) + scaled_gain = int_tofp(100); + + /* + * Actual IIR filter: + * new output = old output * (1 - gain) + input * gain + * + * To Do: Often the actual pstate the system ran at over the last + * interval is not what was asked for, due to influence from + * other CPUs. It might make sense to use the average pstate + * (get_avg_pstate) as the old_output here (as per previous + * work by Philippe Longepe and Stephane Gasparini on the + * get_target_pstate_use_cpu_load method). Test it. + */ + cpu->sample.target = div_u64((int_tofp(100) - scaled_gain) * + cpu->sample.target + scaled_gain * + unfiltered_target, int_tofp(100)); + /* + * Clamp the filtered value. + */ + intel_pstate_get_min_max(cpu, &min_perf, &max_perf); + if (cpu->sample.target < int_tofp(min_perf)) + cpu->sample.target = int_tofp(min_perf); + if (cpu->sample.target > int_tofp(max_perf)) + cpu->sample.target = int_tofp(max_perf); + + return fp_toint(cpu->sample.target + (1 << (FRAC_BITS-1))); } static inline void intel_pstate_update_pstate(struct cpudata *cpu, int pstate) @@ -1579,6 +1656,7 @@ 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)