From: Ionela Voinescu <ionela.voinescu@arm.com> To: Sumit Gupta <sumitg@nvidia.com> Cc: Beata Michalska <beata.michalska@arm.com>, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, sudeep.holla@arm.covm, will@kernel.org, catalin.marinas@arm.com, viresh.kumar@linaro.org, rafael@kernel.org, yang@os.amperecomputing.com, linux-tegra@vger.kernel.org Subject: Re: [PATCH v2 2/2] cpufreq: Wire-up arch-flavored freq info into cpufreq_verify_current_freq Date: Tue, 5 Dec 2023 11:05:09 +0000 [thread overview] Message-ID: <ZW8D5TfSwuJfdYeD@arm.com> (raw) In-Reply-To: <3e6077bb-907c-057f-0896-d0a5814a4229@nvidia.com> Hi Sumit, On Friday 01 Dec 2023 at 18:32:10 (+0530), Sumit Gupta wrote: > Hi Ionela, > > > > --- a/drivers/cpufreq/cpufreq.c > > > +++ b/drivers/cpufreq/cpufreq.c > > > @@ -1756,7 +1756,8 @@ static unsigned int cpufreq_verify_current_freq(struct cpufreq_policy *policy, b > > > { > > > unsigned int new_freq; > > > > > > - new_freq = cpufreq_driver->get(policy->cpu); > > > + new_freq = arch_freq_get_on_cpu(policy->cpu); > > > + new_freq = new_freq ?: cpufreq_driver->get(policy->cpu); > > > > Given that arch_freq_get_on_cpu() is an average frequency, it does not > > seem right to me to trigger the sync & update process of > > cpufreq_verify_current_freq() based on it. > > > > cpufreq_verify_current_freq() will at least modify the internal state of > > the policy and send PRE and POST notifications, if not do a full frequency > > update, based on this average frequency, which is likely different from > > the current frequency, even beyond the 1MHz threshold. > > > > While I believe it's okay to return this average frequency in > > cpuinfo_cur_freq, I don't think it should be used as an indication of > > an accurate current frequency, which is what > > cpufreq_verify_current_freq() expects. > > > > Sumit, can you give more details on the issue at [1] and why this change > > fixes it? > > > > [1] https://lore.kernel.org/lkml/6a5710f6-bfbb-5dfd-11cd-0cd02220cee7@nvidia.com/ > > > > Thank you, > > Ionela. > > > cpufreq_verify_current_freq() also updates 'policy->cur' in POST > notification if the frequency from hardware has more delta (out of sync). > > As the value from 'cpufreq_driver->get()' is not reliable due to [1], > calling the 'get' hook can update the 'policy->cur' with a wrong value when > governor starts in cpufreq_start_governor(). > And if the frequency is never changed after the governor starts during > boot e.g. when performance governor is set as default, then > 'scaling_cur_freq' always returns wrong value. > > Instead, the arch_freq_get_on_cpu() API updates 'policy->cur' with a more > stable freq value. > > [1] https://lore.kernel.org/lkml/20230418113459.12860-7-sumitg@nvidia.com/ Got it, many thanks! As the code is right now in v2, arch_freq_get_on_cpu() is called on show_scaling_cur_freq(), so the problem you describe would not show up. policy->cur would still be incorrect, but 'scaling_cur_freq' would return the value from arch_freq_get_on_cpu(). Would it be enough if arch_freq_get_on_cpu() gets also called from show_cpuinfo_cur_freq() instead of cpufreq_verify_current_freq()? Thanks, Ionela. > > Best regards, > Sumit Gupta > > > > if (!new_freq) > > > return 0; > > > > > > -- > > > 2.25.1 > > >
WARNING: multiple messages have this Message-ID (diff)
From: Ionela Voinescu <ionela.voinescu@arm.com> To: Sumit Gupta <sumitg@nvidia.com> Cc: Beata Michalska <beata.michalska@arm.com>, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, sudeep.holla@arm.covm, will@kernel.org, catalin.marinas@arm.com, viresh.kumar@linaro.org, rafael@kernel.org, yang@os.amperecomputing.com, linux-tegra@vger.kernel.org Subject: Re: [PATCH v2 2/2] cpufreq: Wire-up arch-flavored freq info into cpufreq_verify_current_freq Date: Tue, 5 Dec 2023 11:05:09 +0000 [thread overview] Message-ID: <ZW8D5TfSwuJfdYeD@arm.com> (raw) In-Reply-To: <3e6077bb-907c-057f-0896-d0a5814a4229@nvidia.com> Hi Sumit, On Friday 01 Dec 2023 at 18:32:10 (+0530), Sumit Gupta wrote: > Hi Ionela, > > > > --- a/drivers/cpufreq/cpufreq.c > > > +++ b/drivers/cpufreq/cpufreq.c > > > @@ -1756,7 +1756,8 @@ static unsigned int cpufreq_verify_current_freq(struct cpufreq_policy *policy, b > > > { > > > unsigned int new_freq; > > > > > > - new_freq = cpufreq_driver->get(policy->cpu); > > > + new_freq = arch_freq_get_on_cpu(policy->cpu); > > > + new_freq = new_freq ?: cpufreq_driver->get(policy->cpu); > > > > Given that arch_freq_get_on_cpu() is an average frequency, it does not > > seem right to me to trigger the sync & update process of > > cpufreq_verify_current_freq() based on it. > > > > cpufreq_verify_current_freq() will at least modify the internal state of > > the policy and send PRE and POST notifications, if not do a full frequency > > update, based on this average frequency, which is likely different from > > the current frequency, even beyond the 1MHz threshold. > > > > While I believe it's okay to return this average frequency in > > cpuinfo_cur_freq, I don't think it should be used as an indication of > > an accurate current frequency, which is what > > cpufreq_verify_current_freq() expects. > > > > Sumit, can you give more details on the issue at [1] and why this change > > fixes it? > > > > [1] https://lore.kernel.org/lkml/6a5710f6-bfbb-5dfd-11cd-0cd02220cee7@nvidia.com/ > > > > Thank you, > > Ionela. > > > cpufreq_verify_current_freq() also updates 'policy->cur' in POST > notification if the frequency from hardware has more delta (out of sync). > > As the value from 'cpufreq_driver->get()' is not reliable due to [1], > calling the 'get' hook can update the 'policy->cur' with a wrong value when > governor starts in cpufreq_start_governor(). > And if the frequency is never changed after the governor starts during > boot e.g. when performance governor is set as default, then > 'scaling_cur_freq' always returns wrong value. > > Instead, the arch_freq_get_on_cpu() API updates 'policy->cur' with a more > stable freq value. > > [1] https://lore.kernel.org/lkml/20230418113459.12860-7-sumitg@nvidia.com/ Got it, many thanks! As the code is right now in v2, arch_freq_get_on_cpu() is called on show_scaling_cur_freq(), so the problem you describe would not show up. policy->cur would still be incorrect, but 'scaling_cur_freq' would return the value from arch_freq_get_on_cpu(). Would it be enough if arch_freq_get_on_cpu() gets also called from show_cpuinfo_cur_freq() instead of cpufreq_verify_current_freq()? Thanks, Ionela. > > Best regards, > Sumit Gupta > > > > if (!new_freq) > > > return 0; > > > > > > -- > > > 2.25.1 > > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2023-12-05 11:05 UTC|newest] Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top 2023-11-27 16:08 [PATCH v2 0/2] Add support for AArch64 AMUv1-based arch_freq_get_on_cpu Beata Michalska 2023-11-27 16:08 ` Beata Michalska 2023-11-27 16:08 ` [PATCH v2 1/2] arm64: Provide an AMU-based version of arch_freq_get_on_cpu Beata Michalska 2023-11-27 16:08 ` Beata Michalska 2023-11-28 15:13 ` Ionela Voinescu 2023-11-28 15:13 ` Ionela Voinescu 2024-02-02 9:20 ` Beata Michalska 2024-02-02 9:20 ` Beata Michalska 2024-02-22 19:55 ` Vanshidhar Konda 2024-02-22 19:55 ` Vanshidhar Konda 2023-11-27 16:08 ` [PATCH v2 2/2] cpufreq: Wire-up arch-flavored freq info into cpufreq_verify_current_freq Beata Michalska 2023-11-27 16:08 ` Beata Michalska 2023-11-28 14:01 ` Ionela Voinescu 2023-11-28 14:01 ` Ionela Voinescu 2023-12-01 13:02 ` Sumit Gupta 2023-12-01 13:02 ` Sumit Gupta 2023-12-05 11:05 ` Ionela Voinescu [this message] 2023-12-05 11:05 ` Ionela Voinescu 2023-12-06 13:28 ` Sumit Gupta 2023-12-06 13:28 ` Sumit Gupta 2023-12-07 9:22 ` Ionela Voinescu 2023-12-07 9:22 ` Ionela Voinescu 2023-12-08 15:34 ` Sumit Gupta 2023-12-08 15:34 ` Sumit Gupta 2024-02-02 9:14 ` Beata Michalska 2024-02-02 9:14 ` Beata Michalska 2023-12-06 20:41 ` Rafael J. Wysocki 2023-12-06 20:41 ` Rafael J. Wysocki 2024-02-02 9:05 ` Beata Michalska 2024-02-02 9:05 ` Beata Michalska
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