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[103.229.16.4]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2aece56cdf4sm128855745ad.8.2026.03.16.01.38.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 16 Mar 2026 01:38:11 -0700 (PDT) Message-ID: <20c1e58c-bbd8-49b0-bda0-91e3459134dd@oss.qualcomm.com> Date: Mon, 16 Mar 2026 16:38:07 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] cpufreq: optimize policy_is_shared() To: Yury Norov , "Rafael J. Wysocki" , Viresh Kumar , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Yury Norov , zhongqiu.han@oss.qualcomm.com References: <20260314192544.605914-1-ynorov@nvidia.com> Content-Language: en-US From: Zhongqiu Han In-Reply-To: <20260314192544.605914-1-ynorov@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzE2MDA2NCBTYWx0ZWRfX4uY2OkEyENDP wONUBtWplh33lnWq9ry3SDD8kfAjP0W01M8zRrE3ndgERj0232N+n0B+Z9rbCpq3/mc5uvNnP/i +c2yqS2y8+gTYq+rIK89TcJLK0g2HZONmNaJShOUy13ZjlZFDotHO0xcGiYWLWSvWlTHIgN5svq fgMrxK/tMvylHzlJoZBJJdaa2e1U0PPV12sflEa3iw74+rLQ4GWYyVddEerJw9heu5gv3BCKVrV u4GDCeO9BrAPFaT2cI5cwEuU7TA0lECJaVy8YYXQMEg65UkJuueKJHcUBCsJltjBtJzQDBB5zBp d9FCVMnVRbw9Fnkdob3HnDpNMl0M/u6BGx1QI8gpPEyGkiea251Lx5fMMCOjDT/flsIRoBbUkrs MxmDhItHLCSVrYqsn/9RiW9YYnW48oV9OxUEee+69oOhKnU6QRmKY4IjobAQtdxdFuvp4e55Rid nGUkv2x+oVfmALNBotg== X-Proofpoint-GUID: ZtotE9o2OEicAKmxgUsJF3iSWaBzsJFh X-Authority-Analysis: v=2.4 cv=fLs0HJae c=1 sm=1 tr=0 ts=69b7c175 cx=c_pps a=IZJwPbhc+fLeJZngyXXI0A==:117 a=nuhDOHQX5FNHPW3J6Bj6AA==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=yOCtJkima9RkubShWh1s:22 a=VwQbUJbxAAAA:8 a=Ikd4Dj_1AAAA:8 a=407Z2pdP_-DL_vujbKgA:9 a=QEXdDO2ut3YA:10 a=uG9DUKGECoFWVXl0Dc02:22 X-Proofpoint-ORIG-GUID: ZtotE9o2OEicAKmxgUsJF3iSWaBzsJFh X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-16_03,2026-03-13_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 malwarescore=0 lowpriorityscore=0 suspectscore=0 impostorscore=0 clxscore=1015 adultscore=0 spamscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603160064 On 3/15/2026 3:25 AM, Yury Norov wrote: > The switch to cpumask_nth() over cpumask_weight(), as it may return > earlier - as soon as the function counts the required number of CPUs. > > Signed-off-by: Yury Norov > --- > include/linux/cpufreq.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/include/linux/cpufreq.h b/include/linux/cpufreq.h > index cc894fc38971..8ca2bcb3d7ae 100644 > --- a/include/linux/cpufreq.h > +++ b/include/linux/cpufreq.h > @@ -232,7 +232,7 @@ static inline bool policy_is_inactive(struct cpufreq_policy *policy) > > static inline bool policy_is_shared(struct cpufreq_policy *policy) > { > - return cpumask_weight(policy->cpus) > 1; > + return cpumask_nth(1, policy->cpus) < nr_cpumask_bits; > } > > #ifdef CONFIG_CPU_FREQ Hi Yury, Thanks for the patch. I see the intent of switching from cpumask_weight() to cpumask_nth() to allow an early exit once we know there are at least two CPUs in the mask. Functionally this looks equivalent. That said, policy_is_shared() appears to be used mostly during governor /driver bring-up paths (e.g. sugov_start(),cpufreq_dbs_governor_start(), acpi_cpufreq_cpu_init(), etc.), rather than a hot runtime path. Given that, I'm not sure the micro-optimization is worth the readability cost. Also, cpumask_nth()'s documented return value is ">= nr_cpu_ids if such cpu doesn't exist", so comparing against nr_cpu_ids would match the API contract more directly than nr_cpumask_bits (even if they are currently equivalent). [1][2] [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/cpumask.h#n540 [2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/cpumask.h#n78 -- Thx and BRs, Zhongqiu Han