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Mon, 03 Aug 2020 23:26:15 -0700 (PDT) Date: Tue, 4 Aug 2020 11:56:11 +0530 From: Viresh Kumar To: Ionela Voinescu Cc: rjw@rjwysocki.net, dietmar.eggemann@arm.com, catalin.marinas@arm.com, sudeep.holla@arm.com, will@kernel.org, linux@armlinux.org.uk, mingo@redhat.com, peterz@infradead.org, linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/7] cpufreq: set invariance scale factor on transition end Message-ID: <20200804062611.6jpra73hmhybdw3i@vireshk-mac-ubuntu> References: <20200722093732.14297-1-ionela.voinescu@arm.com> <20200722093732.14297-3-ionela.voinescu@arm.com> <20200730041334.cjg5mc5xpopd2lst@vireshk-mac-ubuntu> <20200803135838.GB9512@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200803135838.GB9512@arm.com> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03-08-20, 14:58, Ionela Voinescu wrote: > Hi Viresh, > > On Thursday 30 Jul 2020 at 09:43:34 (+0530), Viresh Kumar wrote: > > On 22-07-20, 10:37, Ionela Voinescu wrote: > > > While the move of the invariance setter calls (arch_set_freq_scale()) > > > from cpufreq drivers to cpufreq core maintained the previous > > > functionality for existing drivers that use target_index() and > > > fast_switch() for frequency switching, it also gives the possibility > > > of adding support for users of the target() callback, which is exploited > > > here. > > > > > > To be noted that the target() callback 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, > > > gx-suspmod.c:439:2: .target = cpufreq_gx_target, > > > pcc-cpufreq.c:573:2: .target = pcc_cpufreq_target, > > > > > > Similarly to the path taken for target_index() calls in the cpufreq core > > > during a frequency change, all of the drivers above will mark the end of a > > > frequency change by a call to cpufreq_freq_transition_end(). > > > > > > Therefore, cpufreq_freq_transition_end() can be used as the location for > > > the arch_set_freq_scale() call to potentially inform the scheduler of the > > > frequency change. > > > > > > This change maintains the previous functionality for the drivers that > > > implement the target_index() callback, while also adding support for the > > > few drivers that implement the deprecated target() callback. > > > > > > Two notes are worthwhile here: > > > - In __target_index(), cpufreq_freq_transition_end() is called only for > > > drivers that have synchronous notifications enabled. There is only one > > > driver that disables them, > > > > > > drivers/cpufreq/powernow-k8.c:1142: .flags = CPUFREQ_ASYNC_NOTIFICATION, > > > > > > which is deprecated. > > > > I don't think this is deprecated. Heh, maybe I misunderstood. I thought you are talking about the flag, while you were talking about the driver. > Sorry, possibly 'deprecated' is a strong word. > > As far as I knew acpi_cpufreq was recommended more recently for K8/K10 > CPUs so that's why I decided not to create a special case for it, also > considering that it was not supporting cpufreq-based frequency > invariance to begin with. > > We could support this as well by having a call to arch_set_freq_scale() > on the else path in __target_index(). But given that there was only this > one user of CPUFREQ_ASYNC_NOTIFICATION, I thought I'd propose this simpler > version first. > > Let me know if my reasoning is wrong. Nevertheless, I don't think you need to mention this detail in changelog for powernow-k8 as cpufreq_freq_transition_end() does get called for it as well, by the driver instead of the core. -- viresh