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smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com 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 9D0DB1063; Thu, 23 Jan 2025 13:38:40 -0800 (PST) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 3544A3F66E; Thu, 23 Jan 2025 13:38:09 -0800 (PST) Date: Thu, 23 Jan 2025 22:37:29 +0100 From: Beata Michalska To: Vanshidhar Konda Cc: Viresh Kumar , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-pm@vger.kernel.org, ionela.voinescu@arm.com, sudeep.holla@arm.com, will@kernel.org, catalin.marinas@arm.com, rafael@kernel.org, sumitg@nvidia.com, yang@os.amperecomputing.com, lihuisong@huawei.com, zhanjie9@hisilicon.com Subject: Re: [PATCH v9 1/5] cpufreq: Allow arch_freq_get_on_cpu to return an error Message-ID: References: <20250121084435.2839280-1-beata.michalska@arm.com> <20250121084435.2839280-2-beata.michalska@arm.com> <20250121104706.2gcegucb6hcuksrd@vireshk-i7> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Jan 21, 2025 at 10:40:55AM -0800, Vanshidhar Konda wrote: > On Tue, Jan 21, 2025 at 04:14:32PM +0100, Beata Michalska wrote: > > On Tue, Jan 21, 2025 at 04:17:06PM +0530, Viresh Kumar wrote: > > > On 21-01-25, 08:44, Beata Michalska wrote: > > > > Allow arch_freq_get_on_cpu to return an error for cases when retrieving > > > > current CPU frequency is not possible, whether that being due to lack of > > > > required arch support or due to other circumstances when the current > > > > frequency cannot be determined at given point of time. > > > > > > > > Signed-off-by: Beata Michalska > > > > --- > > > > arch/x86/kernel/cpu/aperfmperf.c | 2 +- > > > > arch/x86/kernel/cpu/proc.c | 7 +++++-- > > > > drivers/cpufreq/cpufreq.c | 8 ++++---- > > > > include/linux/cpufreq.h | 2 +- > > > > 4 files changed, 11 insertions(+), 8 deletions(-) > > > > > > > > diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c > > > > index f642de2ebdac..6cf31a1649c4 100644 > > > > --- a/arch/x86/kernel/cpu/aperfmperf.c > > > > +++ b/arch/x86/kernel/cpu/aperfmperf.c > > > > @@ -498,7 +498,7 @@ void arch_scale_freq_tick(void) > > > > */ > > > > #define MAX_SAMPLE_AGE ((unsigned long)HZ / 50) > > > > > > > > -unsigned int arch_freq_get_on_cpu(int cpu) > > > > +int arch_freq_get_on_cpu(int cpu) > > > > { > > > > struct aperfmperf *s = per_cpu_ptr(&cpu_samples, cpu); > > > > unsigned int seq, freq; > > > > diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c > > > > index 41ed01f46bd9..d79f5845a463 100644 > > > > --- a/arch/x86/kernel/cpu/proc.c > > > > +++ b/arch/x86/kernel/cpu/proc.c > > > > @@ -86,9 +86,12 @@ static int show_cpuinfo(struct seq_file *m, void *v) > > > > seq_printf(m, "microcode\t: 0x%x\n", c->microcode); > > > > > > > > if (cpu_has(c, X86_FEATURE_TSC)) { > > > > - unsigned int freq = arch_freq_get_on_cpu(cpu); > > > > + int freq = arch_freq_get_on_cpu(cpu); > > > > > > > > - seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000)); > > > > + if (freq <= 0) > > > > + seq_puts(m, "cpu MHz\t\t: Unknown\n"); > > > > + else > > > > + seq_printf(m, "cpu MHz\t\t: %u.%03u\n", freq / 1000, (freq % 1000)); > > > > } > > > > > > > > /* Cache size */ > > > > diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c > > > > index 418236fef172..6f45684483c4 100644 > > > > --- a/drivers/cpufreq/cpufreq.c > > > > +++ b/drivers/cpufreq/cpufreq.c > > > > @@ -728,18 +728,18 @@ show_one(cpuinfo_transition_latency, cpuinfo.transition_latency); > > > > show_one(scaling_min_freq, min); > > > > show_one(scaling_max_freq, max); > > > > > > > > -__weak unsigned int arch_freq_get_on_cpu(int cpu) > > > > +__weak int arch_freq_get_on_cpu(int cpu) > > > > { > > > > - return 0; > > > > + return -EOPNOTSUPP; > > > > } > > > > > > > > static ssize_t show_scaling_cur_freq(struct cpufreq_policy *policy, char *buf) > > > > { > > > > ssize_t ret; > > > > - unsigned int freq; > > > > + int freq; > > > > > > > > freq = arch_freq_get_on_cpu(policy->cpu); > > > > - if (freq) > > > > + if (freq > 0) > > > > > > >= ? > > > > > > Since we can return error now, 0 should be considered a valid > > > frequency value ? > > Theoretically speaking - it should, though what would 0 actually > > represent then ? > I would think the value of 0 would be valid and should be interpreted in a > product/architecture specific manner? From silicon behavior, to me only negative > frequency values wouldn't make any sense. Still not convinced as of when '0' could represent a valid frequency and what that one would actually imply but I do not have that strong of an opinion here. > > In Patch 1 of this series we interpret 0 as "Unknown" on a x86 system though. So > for the sake of consistency should we consider 0 a valid value everywhere? Yes, but on the other hand, showing 'Unknown' could be skipped entirely here as the arch_freq_get_on_cpu for x86 is always providing a 'valid' frequency. The change here was just to make things somewhat sane. Note that the new attribute introduced in the following patch will utilise potential error values from arch_freq_get_on_cpu though. --- BR Beata > > Regards, > Vanshi > > > > > --- > > BR > > Beata > > > > > > > ret = sysfs_emit(buf, "%u\n", freq); > > > > else if (cpufreq_driver->setpolicy && cpufreq_driver->get) > > > > ret = sysfs_emit(buf, "%u\n", cpufreq_driver->get(policy->cpu)); > > > > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h > > > > index 7fe0981a7e46..02fd4746231d 100644 > > > > --- a/include/linux/cpufreq.h > > > > +++ b/include/linux/cpufreq.h > > > > @@ -1184,7 +1184,7 @@ static inline int of_perf_domain_get_sharing_cpumask(int pcpu, const char *list_ > > > > } > > > > #endif > > > > > > > > -extern unsigned int arch_freq_get_on_cpu(int cpu); > > > > +extern int arch_freq_get_on_cpu(int cpu); > > > > > > > > #ifndef arch_set_freq_scale > > > > static __always_inline > > > > -- > > > > 2.25.1 > > > > > > -- > > > viresh