Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753899AbcKNUoh (ORCPT ); Mon, 14 Nov 2016 15:44:37 -0500 Received: from mail-qt0-f193.google.com ([209.85.216.193]:33016 "EHLO mail-qt0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751975AbcKNUof (ORCPT ); Mon, 14 Nov 2016 15:44:35 -0500 MIME-Version: 1.0 In-Reply-To: <691e286d-249b-e450-2df1-8421d83e6a46@semaphore.gr> References: <691e286d-249b-e450-2df1-8421d83e6a46@semaphore.gr> From: "Rafael J. Wysocki" Date: Mon, 14 Nov 2016 21:44:33 +0100 X-Google-Sender-Auth: FVRdd3JyRfu3xh_cI_WRkPD3GEc Message-ID: Subject: Re: [PATCH v2] cpufreq: conservative: Decrease frequency faster when the update deferred To: Stratos Karafotis Cc: "Rafael J. Wysocki" , Viresh Kumar , "linux-pm@vger.kernel.org" , LKML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 12079 Lines: 220 On Sat, Nov 12, 2016 at 10:04 PM, Stratos Karafotis wrote: > Conservative governor changes the CPU frequency in steps. > That means that if a CPU runs at max frequency, it will need several > sampling periods to return to min frequency when the workload > is finished. > > If the update function that calculates the load and target frequency > is deferred, the governor might need even more time to decrease the > frequency. > > This may have impact to power consumption and after all conservative > should decrease the frequency if there is no workload at every sampling > rate. > > To resolve the above issue calculate the number of sampling periods > that the update is deferred. Considering that for each sampling period > conservative should drop the frequency by a freq_step because the > CPU was idle apply the proper subtraction to requested frequency. > > Below, the kernel trace with and without this patch. First an > intensive workload is applied on a specific CPU. Then the workload > is removed and the CPU goes to idle. > > WITHOUT > > -0 [007] dN.. 620.329153: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 620.350857: cpu_frequency: state=1700000 cpu_id=7 > kworker/7:2-556 [007] .... 620.370856: cpu_frequency: state=1900000 cpu_id=7 > kworker/7:2-556 [007] .... 620.390854: cpu_frequency: state=2100000 cpu_id=7 > kworker/7:2-556 [007] .... 620.411853: cpu_frequency: state=2200000 cpu_id=7 > kworker/7:2-556 [007] .... 620.432854: cpu_frequency: state=2400000 cpu_id=7 > kworker/7:2-556 [007] .... 620.453854: cpu_frequency: state=2600000 cpu_id=7 > kworker/7:2-556 [007] .... 620.494856: cpu_frequency: state=2900000 cpu_id=7 > kworker/7:2-556 [007] .... 620.515856: cpu_frequency: state=3100000 cpu_id=7 > kworker/7:2-556 [007] .... 620.536858: cpu_frequency: state=3300000 cpu_id=7 > kworker/7:2-556 [007] .... 620.557857: cpu_frequency: state=3401000 cpu_id=7 > -0 [007] d... 669.591363: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 669.591939: cpu_idle: state=4294967295 cpu_id=7 > -0 [007] d... 669.591980: cpu_idle: state=4 cpu_id=7 > -0 [007] dN.. 669.591989: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 670.201224: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 670.221975: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 670.222016: cpu_frequency: state=3300000 cpu_id=7 > -0 [007] d... 670.222026: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 670.234964: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 670.801251: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 671.236046: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 671.236073: cpu_frequency: state=3100000 cpu_id=7 > -0 [007] d... 671.236112: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 671.393437: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 671.401277: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 671.404083: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 671.404111: cpu_frequency: state=2900000 cpu_id=7 > -0 [007] d... 671.404125: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 671.404974: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 671.501180: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 671.995414: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 671.995459: cpu_frequency: state=2800000 cpu_id=7 > -0 [007] d... 671.995469: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 671.996287: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 672.001305: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 672.078374: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 672.078410: cpu_frequency: state=2600000 cpu_id=7 > -0 [007] d... 672.078419: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 672.158020: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 672.158040: cpu_frequency: state=2400000 cpu_id=7 > -0 [007] d... 672.158044: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 672.160038: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 672.234557: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 672.237121: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 672.237174: cpu_frequency: state=2100000 cpu_id=7 > -0 [007] d... 672.237186: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 672.237778: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 672.267902: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 672.269860: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 672.269906: cpu_frequency: state=1900000 cpu_id=7 > -0 [007] d... 672.269914: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 672.271902: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 672.751342: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 672.823056: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-556 [007] .... 672.823095: cpu_frequency: state=1600000 cpu_id=7 > > WITH > > -0 [007] dN.. 4380.928009: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-399 [007] .... 4380.949767: cpu_frequency: state=2000000 cpu_id=7 > kworker/7:2-399 [007] .... 4380.969765: cpu_frequency: state=2200000 cpu_id=7 > kworker/7:2-399 [007] .... 4381.009766: cpu_frequency: state=2500000 cpu_id=7 > kworker/7:2-399 [007] .... 4381.029767: cpu_frequency: state=2600000 cpu_id=7 > kworker/7:2-399 [007] .... 4381.049769: cpu_frequency: state=2800000 cpu_id=7 > kworker/7:2-399 [007] .... 4381.069769: cpu_frequency: state=3000000 cpu_id=7 > kworker/7:2-399 [007] .... 4381.089771: cpu_frequency: state=3100000 cpu_id=7 > kworker/7:2-399 [007] .... 4381.109772: cpu_frequency: state=3400000 cpu_id=7 > kworker/7:2-399 [007] .... 4381.129773: cpu_frequency: state=3401000 cpu_id=7 > -0 [007] d... 4428.226159: cpu_idle: state=1 cpu_id=7 > -0 [007] d... 4428.226176: cpu_idle: state=4294967295 cpu_id=7 > -0 [007] d... 4428.226181: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 4428.227177: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 4428.551640: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 4428.649239: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-399 [007] .... 4428.649268: cpu_frequency: state=2800000 cpu_id=7 > -0 [007] d... 4428.649278: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 4428.689856: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 4428.799542: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 4428.801683: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-399 [007] .... 4428.801748: cpu_frequency: state=1700000 cpu_id=7 > -0 [007] d... 4428.801761: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 4428.806545: cpu_idle: state=4294967295 cpu_id=7 > ... > -0 [007] d... 4429.051880: cpu_idle: state=4 cpu_id=7 > -0 [007] d... 4429.086240: cpu_idle: state=4294967295 cpu_id=7 > kworker/7:2-399 [007] .... 4429.086293: cpu_frequency: state=1600000 cpu_id=7 > > Without the patch the CPU dropped to min frequency after 3.2s > With the patch applied the CPU dropped to min frequency after 0.86s > > Signed-off-by: Stratos Karafotis > --- > v1 -> v2 > - Use correct terminology in change log > - Change the member variable name from 'deferred_periods' to 'idle_periods' > - Fix format issue > > drivers/cpufreq/cpufreq_conservative.c | 14 +++++++++++++- > drivers/cpufreq/cpufreq_governor.c | 18 +++++++++++++----- > drivers/cpufreq/cpufreq_governor.h | 1 + > 3 files changed, 27 insertions(+), 6 deletions(-) > > diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c > index fa5ece3..d787772 100644 > --- a/drivers/cpufreq/cpufreq_conservative.c > +++ b/drivers/cpufreq/cpufreq_conservative.c > @@ -73,7 +73,19 @@ static unsigned int cs_dbs_update(struct cpufreq_policy *policy) > */ > if (cs_tuners->freq_step == 0) > goto out; > - > + /* > + * Decrease requested_freq for each idle period that we didn't > + * update the frequency > + */ > + if (policy_dbs->idle_periods < UINT_MAX) { > + unsigned int freq_target = policy_dbs->idle_periods * > + get_freq_target(cs_tuners, policy); > + if (requested_freq > freq_target) > + requested_freq -= freq_target; > + else > + requested_freq = policy->min; > + policy_dbs->idle_periods = UINT_MAX; > + } > /* > * If requested_freq is out of range, it is likely that the limits > * changed in the meantime, so fall back to current frequency in that > diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c > index 3729474..1bc7137 100644 > --- a/drivers/cpufreq/cpufreq_governor.c > +++ b/drivers/cpufreq/cpufreq_governor.c > @@ -117,7 +117,7 @@ unsigned int dbs_update(struct cpufreq_policy *policy) > struct policy_dbs_info *policy_dbs = policy->governor_data; > struct dbs_data *dbs_data = policy_dbs->dbs_data; > unsigned int ignore_nice = dbs_data->ignore_nice_load; > - unsigned int max_load = 0; > + unsigned int max_load = 0, idle_periods = UINT_MAX; > unsigned int sampling_rate, io_busy, j; > > /* > @@ -163,8 +163,12 @@ unsigned int dbs_update(struct cpufreq_policy *policy) > * calls, so the previous load value can be used then. > */ > load = j_cdbs->prev_load; > - } else if (unlikely(time_elapsed > 2 * sampling_rate && > - j_cdbs->prev_load)) { > + } else if (unlikely(time_elapsed > 2 * sampling_rate)) { > + unsigned int periods = time_elapsed / sampling_rate; > + > + if (periods < idle_periods) > + idle_periods = periods; > + > /* > * If the CPU had gone completely idle and a task has > * just woken up on this CPU now, it would be unfair to > @@ -189,8 +193,10 @@ unsigned int dbs_update(struct cpufreq_policy *policy) > * 'time_elapsed' (as compared to the sampling rate) > * indicates this scenario. > */ > - load = j_cdbs->prev_load; > - j_cdbs->prev_load = 0; > + if (j_cdbs->prev_load) { > + load = j_cdbs->prev_load; > + j_cdbs->prev_load = 0; > + } > } else { > if (time_elapsed >= idle_time) { > load = 100 * (time_elapsed - idle_time) / time_elapsed; > @@ -218,6 +224,8 @@ unsigned int dbs_update(struct cpufreq_policy *policy) > if (load > max_load) > max_load = load; > } > + policy_dbs->idle_periods = idle_periods; > + > return max_load; > } > EXPORT_SYMBOL_GPL(dbs_update); I have a murky suspicion that the changes in dbs_update() are going to break something. I need to recall what it was, though. Thanks, Rafael