From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lukasz Majewski Subject: Re: [PATCH v4 5/7] cpufreq: Calculate number of busy CPUs Date: Thu, 27 Jun 2013 12:58:19 +0200 Message-ID: <20130627125819.5c90da30@amdc308.digital.local> References: <1370502472-7249-1-git-send-email-l.majewski@samsung.com> <1371661969-7660-1-git-send-email-l.majewski@samsung.com> <1371661969-7660-6-git-send-email-l.majewski@samsung.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: Received: from mailout4.samsung.com ([203.254.224.34]:31692 "EHLO mailout4.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752410Ab3F0K63 (ORCPT ); Thu, 27 Jun 2013 06:58:29 -0400 In-reply-to: Sender: linux-pm-owner@vger.kernel.org List-Id: linux-pm@vger.kernel.org To: Viresh Kumar , "Rafael J. Wysocky" Cc: "cpufreq@vger.kernel.org" , Linux PM list , Vincent Guittot , Jonghwa Lee , Myungjoo Ham , linux-kernel , Lukasz Majewski , Andre Przywara , Daniel Lezcano , Kukjin Kim , Zhang Rui , Eduardo Valentin On Thu, 27 Jun 2013 15:06:43 +0530, Viresh Kumar wrote: > On 19 June 2013 22:42, Lukasz Majewski wrote: > > In the core governor code, per cpu load value is calculated. This > > patch uses it to mark processor as a "busy" one, when load value is > > higher than 90%. > > How can we take this assumption. What about a cpu which is only 70-80% > busy [*]? Do you have any idea of how to precisely set the load threshold? As a side note: I've thought about this patch for some time and for me it looks like we are mixing policy (number of busy CPUs) with abilities, which shall be provided by the driver (boost). Additionally, we can only roughly "estimate" [*] when boost shall run and when it shall be turned off. I think that, we shall leave this management [*] to the thermal framework. This framework is designed exactly to protect from over heating (it uses the same freq_table for passive CPU cooling) with several trip points -> e.g. 40 deg (disable boost), 75 deg (impose max freq as 1.0 GHz to cool down, 90 deg (shutdown immediately). Please refer to PATH v4 7/7. Unfortunately, since we dropped Kconfig flag for BOOST we cannot impose "select THERMAL_FRAMEWORK", when flag for BOOST is enabled at Kconfig. Ideally kernel shall not even build when CONFIG_CPUFREQ_BOOST Kconfig flag is set and thermal for target architecture is not correctly configured (including proper trip points). > So, we would be running at around 70% of policy->max.. Now at > this point you want to enable boost frequency and so that will happen > for all cores... Wouldn't that burn your chip? As I've written above, we can only estimate here. Even with the same manufacturer at one SoC revision BOOST will work with 95% of policy max but the other revision will work stable only with 70%. > > > New cpufreq sysfs attribute is created (busy_cpus). It is read only > > and provides information about number of actually busy CPU. > > Not required. This attribute seems helpful for debug. > > > diff --git a/drivers/cpufreq/cpufreq_governor.c > > b/drivers/cpufreq/cpufreq_governor.c index 077cea7..3402533 100644 > > --- a/drivers/cpufreq/cpufreq_governor.c > > +++ b/drivers/cpufreq/cpufreq_governor.c > > @@ -148,6 +148,7 @@ void dbs_check_cpu(struct dbs_data *dbs_data, > > int cpu) continue; > > > > load = 100 * (wall_time - idle_time) / wall_time; > > + cpufreq_set_busy_cpu(j, load > 90 ? 1 : 0); > > do this only when boost is enabled. Please read above side note. > > > if (dbs_data->cdata->governor == GOV_ONDEMAND) { > > int freq_avg = > > __cpufreq_driver_getavg(policy, j); -- Best regards, Lukasz Majewski Samsung R&D Institute Poland (SRPOL) | Linux Platform Group