From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shilpasri G Bhat Subject: [RFC PATCH] Increase in idle power with schedutil Date: Wed, 18 May 2016 18:23:39 +0530 Message-ID: <1463576020-18597-1-git-send-email-shilpa.bhat@linux.vnet.ibm.com> Return-path: Received: from e28smtp09.in.ibm.com ([125.16.236.9]:55430 "EHLO e28smtp09.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751973AbcERMyB (ORCPT ); Wed, 18 May 2016 08:54:01 -0400 Received: from localhost by e28smtp09.in.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 18 May 2016 18:23:58 +0530 Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: rjw@rjwysocki.net Cc: viresh.kumar@linaro.org, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, ego@linux.vnet.ibm.com, shreyas@linux.vnet.ibm.com, akshay.adiga@linux.vnet.ibm.com, linuxppc-dev@ozlabs.org, Shilpasri G Bhat This patch adds driver callback for fast_switch and below observations on schedutil governor are done with this patch. In POWER8 there is a regression observed with schedutil compared to ondemand. With schedutil the frequency is not ramping down and is mostly stuck at max frequency during idle . This is because of the watchdog timer, an RT task which is fired every 4 seconds which results in requesting max frequency. In a completely idle system, when there are no processes running apart from few short running housekeeping tasks (like watchdog) the system is stuck at max frequency due to 'cpufreq_trigger_update()' static inline void cpufreq_trigger_update(u64 time) { cpufreq_update_util(time, ULONG_MAX, 0); } If there is no noise apart from the watchdog timer the cpu is held at max frequency for no good reason. On a 16 core system I can see an increase in 20% idle power with schedutil compared to ondemand governor. Below is the trace with 'sched:sched_switch' and 'power:cpu_frequency' events. Here the watchdog timer that runs for a very small period is requesting Pmax and this gets triggered regularly. -0 19059.992912: sched_switch: prev_comm=swapper/16 prev_state=R ==> next_comm=watchdog/16 watchdog/16-107 19059.992914: cpu_frequency: state=4322000 cpu_id=16 watchdog/16-107 19059.992915: sched_switch: prev_comm=watchdog/16 prev_state=S ==> next_comm=swapper/16 However adding a cpufreq hook in pick_next_task_idle() to decrease the frequency helped to reduce the problem. static inline void cpufreq_trigger_idle(u64 time) { cpufreq_update_util(time, 0, 1); } This might not be the right fix for the problem, however this thread is reporting the other short-comings of cpufreq_trigger_update(). Shilpasri G Bhat (1): cpufreq: powernv: Add fast_switch callback drivers/cpufreq/powernv-cpufreq.c | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) -- 1.9.3