From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andreas Herrmann Subject: Re: [PATCH v2] cpufreq: pcc-cpufreq: Disable dynamic scaling on many-CPU systems Date: Tue, 17 Jul 2018 22:13:23 +0200 Message-ID: <20180717201323.6rwb4yklq46cmtom@suselix> References: <20180717065048.74mmgk4t5utjaa6a@suselix> <306375154.NhdH6AhdAd@aspire.rjw.lan> <5423012.ZZnfdYddaT@aspire.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Return-path: Content-Disposition: inline In-Reply-To: <5423012.ZZnfdYddaT@aspire.rjw.lan> Sender: linux-kernel-owner@vger.kernel.org To: "Rafael J. Wysocki" Cc: linux-pm@vger.kernel.org, "Rafael J. Wysocki" , Peter Zijlstra , Frederic Weisbecker , Viresh Kumar , linux-kernel@vger.kernel.org List-Id: linux-pm@vger.kernel.org On Tue, Jul 17, 2018 at 06:14:58PM +0200, Rafael J. Wysocki wrote: > From: Rafael J. Wysocki > > The firmware interface used by the pcc-cpufreq driver is > fundamentally not scalable and using it for dynamic CPU performance > scaling on systems with many CPUs leads to degraded performance. > > For this reason, disable dynamic CPU performance scaling on systems > with pcc-cpufreq where the number of CPUs present at the driver init > time is greater than 4. Also make the driver print corresponding > complaints to the kernel log. > > Reported-by: Andreas Herrmann > Signed-off-by: Rafael J. Wysocki > --- > > -> v2: Rework the messages printed in the problematic case. I've tested this patch. Effect is as expected: driver loads but use of ondemand governor is not allowed. Sample output: [ 40.757519] pcc-cpufreq: (v1.10.00) driver loaded with frequency limits: 1200 MHz, 2800 MHz [ 40.831705] pcc_cpufreq_init: Too many CPUs, dynamic performance scaling disabled [ 40.898353] pcc_cpufreq_init: Try to enable a different scaling driver through BIOS settings [ 40.972327] pcc_cpufreq_init: and complain to the system vendor [ 41.025620] cpufreq: Can't use ondemand governor as dynamic switching is disallowed. Fallback to performance governor ... [ 41.187928] cpufreq: Can't use ondemand governor as dynamic switching is disallowed. Fallback to performance governor Last message is shown for each online CPU in the system (ie. 120x). Looks good to me. Andreas > --- > drivers/cpufreq/pcc-cpufreq.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > Index: linux-pm/drivers/cpufreq/pcc-cpufreq.c > =================================================================== > --- linux-pm.orig/drivers/cpufreq/pcc-cpufreq.c > +++ linux-pm/drivers/cpufreq/pcc-cpufreq.c > @@ -589,6 +589,15 @@ static int __init pcc_cpufreq_init(void) > return ret; > } > > + if (num_present_cpus() > 4) { > + pcc_cpufreq_driver.flags |= CPUFREQ_NO_AUTO_DYNAMIC_SWITCHING; > + pr_err("%s: Too many CPUs, dynamic performance scaling disabled\n", > + __func__); > + pr_err("%s: Try to enable a different scaling driver through BIOS settings\n", > + __func__); > + pr_err("%s: and complain to the system vendor\n", __func__); > + } > + > ret = cpufreq_register_driver(&pcc_cpufreq_driver); > > return ret; > >