Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751363AbaFCJeD (ORCPT ); Tue, 3 Jun 2014 05:34:03 -0400 Received: from e28smtp05.in.ibm.com ([122.248.162.5]:56551 "EHLO e28smtp05.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750709AbaFCJeA (ORCPT ); Tue, 3 Jun 2014 05:34:00 -0400 Message-ID: <538D9631.9090500@linux.vnet.ibm.com> Date: Tue, 03 Jun 2014 15:02:33 +0530 From: "Srivatsa S. Bhat" User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120828 Thunderbird/15.0 MIME-Version: 1.0 To: Viresh Kumar CC: "Rafael J. Wysocki" , Vaidyanathan Srinivasan , "ego@linux.vnet.ibm.com" , "linux-pm@vger.kernel.org" , Linux Kernel Mailing List Subject: Re: [PATCH] cpufreq: governor: Be friendly towards latency-sensitive bursty workloads References: <20140526205337.1100.55275.stgit@srivatsabhat.in.ibm.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14060309-8256-0000-0000-00000D84EB75 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/03/2014 01:48 PM, Viresh Kumar wrote: > On 27 May 2014 02:23, Srivatsa S. Bhat wrote: > > Looks fine, some nits.. > >> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c >> -void dbs_check_cpu(struct dbs_data *dbs_data, int cpu) >> +void dbs_check_cpu(struct dbs_data *dbs_data, int cpu, >> + unsigned int sampling_rate) > > We don't need to pass a new argument, we can get all the information from > dbs_data alone. Its already done for multiple routines. Let me know if you > find it difficult to figure out.. > Sure, that would be a good improvement. Does something like the patch below look good? I have only compile-tested it. I'll send out the patch with changelog once I finish testing it. Thank you! Regards, Srivatsa S. Bhat ---------------------------------------------------------------------------- diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c index e1c6433..3e8588f 100644 --- a/drivers/cpufreq/cpufreq_governor.c +++ b/drivers/cpufreq/cpufreq_governor.c @@ -36,14 +36,29 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu) struct od_dbs_tuners *od_tuners = dbs_data->tuners; struct cs_dbs_tuners *cs_tuners = dbs_data->tuners; struct cpufreq_policy *policy; + unsigned int sampling_rate; unsigned int max_load = 0; unsigned int ignore_nice; unsigned int j; - if (dbs_data->cdata->governor == GOV_ONDEMAND) + if (dbs_data->cdata->governor == GOV_ONDEMAND) { + struct od_cpu_dbs_info_s *od_dbs_info; + + /* + * Sometimes, the ondemand governor uses an additional + * multiplier to give long delays. So apply this multiplier to + * the 'sampling_rate', so as to keep the wake-up-from-idle + * detection logic a bit conservative. + */ + sampling_rate = od_tuners->sampling_rate; + od_dbs_info = dbs_data->cdata->get_cpu_dbs_info_s(cpu); + sampling_rate *= od_dbs_info->rate_mult; + ignore_nice = od_tuners->ignore_nice_load; - else + } else { + sampling_rate = cs_tuners->sampling_rate; ignore_nice = cs_tuners->ignore_nice_load; + } policy = cdbs->cur_policy; @@ -96,7 +111,29 @@ void dbs_check_cpu(struct dbs_data *dbs_data, int cpu) if (unlikely(!wall_time || wall_time < idle_time)) continue; - load = 100 * (wall_time - idle_time) / wall_time; + /* + * If the CPU had gone completely idle, and a task just woke up + * on this CPU now, it would be unfair to calculate 'load' the + * usual way for this elapsed time-window, because it will show + * near-zero load, irrespective of how CPU intensive the new + * task is. This is undesirable for latency-sensitive bursty + * workloads. + * + * To avoid this, we reuse the 'load' from the previous + * time-window and give this task a chance to start with a + * reasonably high CPU frequency. + * + * Detecting this situation is easy: the governor's deferrable + * timer would not have fired during CPU-idle periods. Hence + * an unusually large 'wall_time' (as compared to the sampling + * rate) indicates this scenario. + */ + if (unlikely(wall_time > (2 * sampling_rate))) { + load = j_cdbs->prev_load; + } else { + load = 100 * (wall_time - idle_time) / wall_time; + j_cdbs->prev_load = load; + } if (load > max_load) max_load = load; @@ -323,6 +360,10 @@ int cpufreq_governor_dbs(struct cpufreq_policy *policy, j_cdbs->cur_policy = policy; j_cdbs->prev_cpu_idle = get_cpu_idle_time(j, &j_cdbs->prev_cpu_wall, io_busy); + j_cdbs->prev_load = 100 * (j_cdbs->prev_cpu_wall - + j_cdbs->prev_cpu_idle) / + j_cdbs->prev_cpu_wall; + if (ignore_nice) j_cdbs->prev_cpu_nice = kcpustat_cpu(j).cpustat[CPUTIME_NICE]; diff --git a/drivers/cpufreq/cpufreq_governor.h b/drivers/cpufreq/cpufreq_governor.h index bfb9ae1..b56552b 100644 --- a/drivers/cpufreq/cpufreq_governor.h +++ b/drivers/cpufreq/cpufreq_governor.h @@ -134,6 +134,7 @@ struct cpu_dbs_common_info { u64 prev_cpu_idle; u64 prev_cpu_wall; u64 prev_cpu_nice; + unsigned int prev_load; struct cpufreq_policy *cur_policy; struct delayed_work work; /* -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/