From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A5BB5C433E0 for ; Wed, 1 Jul 2020 15:28:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 92FD8207D0 for ; Wed, 1 Jul 2020 15:28:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732069AbgGAP1y (ORCPT ); Wed, 1 Jul 2020 11:27:54 -0400 Received: from foss.arm.com ([217.140.110.172]:50272 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732065AbgGAP1y (ORCPT ); Wed, 1 Jul 2020 11:27:54 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 0331F30E; Wed, 1 Jul 2020 08:27:53 -0700 (PDT) Received: from localhost (unknown [10.1.198.53]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 99B1B3F68F; Wed, 1 Jul 2020 08:27:52 -0700 (PDT) Date: Wed, 1 Jul 2020 16:27:51 +0100 From: Ionela Voinescu To: Viresh Kumar Cc: rjw@rjwysocki.net, catalin.marinas@arm.com, sudeep.holla@arm.com, will@kernel.org, linux@armlinux.org.uk, valentin.schneider@arm.com, mingo@redhat.com, peterz@infradead.org, dietmar.eggemann@arm.com, linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/8] cpufreq: move invariance setter calls in cpufreq core Message-ID: <20200701152751.GA29496@arm.com> References: <20200701090751.7543-1-ionela.voinescu@arm.com> <20200701090751.7543-3-ionela.voinescu@arm.com> <20200701095219.gxrkowtukosnfmwp@vireshk-i7> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200701095219.gxrkowtukosnfmwp@vireshk-i7> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-pm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pm@vger.kernel.org Hey, On Wednesday 01 Jul 2020 at 16:16:19 (+0530), Viresh Kumar wrote: > On 01-07-20, 10:07, Ionela Voinescu wrote: > > From: Valentin Schneider > > > > To properly scale its per-entity load-tracking signals, the task scheduler > > needs to be given a frequency scale factor, i.e. some image of the current > > frequency the CPU is running at. Currently, this scale can be computed > > either by using counters (APERF/MPERF on x86, AMU on arm64), or by > > piggy-backing on the frequency selection done by cpufreq. > > > > For the latter, drivers have to explicitly set the scale factor > > themselves, despite it being purely boiler-plate code: the required > > information depends entirely on the kind of frequency switch callback > > implemented by the driver, i.e. either of: target_index(), target(), > > fast_switch() and setpolicy(). > > > > The fitness of those callbacks with regard to driving the Frequency > > Invariance Engine (FIE) is studied below: > > > > target_index() > > ============== > > Documentation states that the chosen frequency "must be determined by > > freq_table[index].frequency". It isn't clear if it *has* to be that > > frequency, or if it can use that frequency value to do some computation > > that ultimately leads to a different frequency selection. All drivers > > go for the former, while the vexpress-spc-cpufreq has an atypical > > implementation. > > > > Thefore, the hook works on the asusmption the core can use > > freq_table[index].frequency. > > > > target() > > ======= > > This has been flagged as deprecated since: > > > > commit 9c0ebcf78fde ("cpufreq: Implement light weight ->target_index() routine") > > > > It also doesn't have that many users: > > > > cpufreq-nforce2.c:371:2: .target = nforce2_target, > > cppc_cpufreq.c:416:2: .target = cppc_cpufreq_set_target, > > pcc-cpufreq.c:573:2: .target = pcc_cpufreq_target, > > > > Should we care about drivers using this hook, we may be able to exploit > > cpufreq_freq_transition_{being, end}(). Otherwise, if FIE support is > > desired in their current state, arch_set_freq_scale() could still be > > called directly by the driver, while CPUFREQ_CUSTOM_SET_FREQ_SCALE > > could be used to mark support for it. > > > > fast_switch() > > ============= > > This callback *has* to return the frequency that was selected. > > > > setpolicy() > > =========== > > This callback does not have any designated way of informing what was the > > end choice. But there are only two drivers using setpolicy(), and none > > of them have current FIE support: > > > > drivers/cpufreq/longrun.c:281: .setpolicy = longrun_set_policy, > > drivers/cpufreq/intel_pstate.c:2215: .setpolicy = intel_pstate_set_policy, > > > > The intel_pstate is known to use counter-driven frequency invariance. > > Same for acpi-cpufreq driver as well ? > The acpi-cpufreq driver defines target_index() and fast_switch() so it should go through the setting in cpufreq core. But x86 does not actually define arch_set_freq_scale() so when called it won't do anything (won't set any frequency scale factor), but rely on counters to set it through the arch_scale_freq_tick(). But this cpufreq functionality could potentially be used. > And I think we should do the freq-invariance thing for all the above categories > nevertheless. > I'm not sure what you mean by this. You mean we should also (try to) set the frequency scale factor for drivers defining setpolicy() and target()? > > If FIE support is desired in their current state, arch_set_freq_scale() > > could still be called directly by the driver, while > > CPUFREQ_CUSTOM_SET_FREQ_SCALE could be used to mark support for it. > > > > Conclusion > > ========== > > > > Given that the significant majority of current FIE enabled drivers use > > callbacks that lend themselves to triggering the setting of the FIE scale > > factor in a generic way, move the invariance setter calls to cpufreq core, > > while filtering drivers that flag custom support using > > CPUFREQ_CUSTOM_SET_FREQ_SCALE. > > > > Signed-off-by: Valentin Schneider > > Signed-off-by: Ionela Voinescu > > Cc: Rafael J. Wysocki > > Cc: Viresh Kumar > > --- > > drivers/cpufreq/cpufreq.c | 20 +++++++++++++++++--- > > 1 file changed, 17 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > > index 0128de3603df..83b58483a39b 100644 > > --- a/drivers/cpufreq/cpufreq.c > > +++ b/drivers/cpufreq/cpufreq.c > > @@ -2046,9 +2046,16 @@ EXPORT_SYMBOL(cpufreq_unregister_notifier); > > unsigned int cpufreq_driver_fast_switch(struct cpufreq_policy *policy, > > unsigned int target_freq) > > { > > + unsigned int freq; > > + > > target_freq = clamp_val(target_freq, policy->min, policy->max); > > + freq = cpufreq_driver->fast_switch(policy, target_freq); > > + > > > + if (freq && !(cpufreq_driver->flags & CPUFREQ_CUSTOM_SET_FREQ_SCALE)) > > + arch_set_freq_scale(policy->related_cpus, freq, > > + policy->cpuinfo.max_freq); > > This needs to be a separate function. > Yes, that would be nicer. > > > > - return cpufreq_driver->fast_switch(policy, target_freq); > > + return freq; > > } > > EXPORT_SYMBOL_GPL(cpufreq_driver_fast_switch); > > > > @@ -2140,7 +2147,7 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy, > > unsigned int relation) > > { > > unsigned int old_target_freq = target_freq; > > - int index; > > + int index, retval; > > > > if (cpufreq_disabled()) > > return -ENODEV; > > @@ -2171,7 +2178,14 @@ int __cpufreq_driver_target(struct cpufreq_policy *policy, > > > > index = cpufreq_frequency_table_target(policy, target_freq, relation); > > > > - return __target_index(policy, index); > > + retval = __target_index(policy, index); > > + > > + if (!retval && !(cpufreq_driver->flags & CPUFREQ_CUSTOM_SET_FREQ_SCALE)) > > + arch_set_freq_scale(policy->related_cpus, > > + policy->freq_table[index].frequency, > > policy->cur gets updated for both target and target_index type drivers. You can > use that safely. It gets updated after the postchange notification. > This would allow us to cover the drivers that define target() as well (not only target_index() and fast_switch()). Looking over the code we only take that path (calling cpufreq_freq_transition_end()), for !CPUFREQ_ASYNC_NOTIFICATION. But again, that's only used for powernow-k8 which is deprecated. I'll attempt a nice way to use this. Thank you very much for the review, Ionela. > > + policy->cpuinfo.max_freq); > > + > > + return retval; > > } > > EXPORT_SYMBOL_GPL(__cpufreq_driver_target); > > -- > viresh