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[103.229.16.4]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3a853c88aa7sm3667676a91.5.2026.10.06.01.22.52 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 06 Oct 2026 01:22:56 -0700 (PDT) Message-ID: Date: Tue, 6 Oct 2026 16:22:49 +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: schedutil: Serialize start against rate limit updates To: Hui Su , "Rafael J . Wysocki" , Viresh Kumar Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, zhongqiu.han@oss.qualcomm.com References: <20260929103635.3780346-1-sh_def@163.com> Content-Language: en-US From: Zhongqiu Han In-Reply-To: <20260929103635.3780346-1-sh_def@163.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDA2MDAzMyBTYWx0ZWRfX9wz794a1si/E q2bTqSLsA857fKb1tEfNdGEkrqpkLIRHDvsbUzcLC2ry4OVsaCinSx6Gv02a8JP1dI0MzBEsp3Z 1tUG42mPdJMKccJSK2KVTyR0DSmm55ffGcHSBpA6dzfT1m723hXRvMl/WwxwEN3M5ZBT0Nm5ddp MOJCdpw10KhCr7OrzAqxZTwOelfwkcTsjHHgpCq0CU0JUhSdn/TDtxGHpWxv3X5Jc9vXFneB1g6 WCBV9XUeHjVJ8rrEKCzfYSCBBmaxlzR1iEPhgwQnK7WBX9W1uZttbBRDkEZuJxW8JJBKi6X8fRs 7QVUUS6/8Qcly1PQlLUxo/uozmLCcgFQwjPANaW456ECdK8y4cKxvQk50i/nAjMgqZZFhsAlGR/ etxz3e+jd7q5oTHIHUyhdNinZ83yuSuXQFvC7hMNMLRDAulESnzQC3Sr2/zAaR3D+9lQ1t631IY go58TrJuhBJmhet1/kQ== X-Proofpoint-Spam-Info: AW1haW4tMjYxMDA2MDAzMyBTYWx0ZWRfXxETXsfHGwA9i Imge5AOhbz6+VFQQYAY4Jd+4QPqROWc8hw3nPHkYSfJOGekM4EOk/BnSlpe0DUJsH3n0lzkJ8E8 wCZph7T/gPtuG8tLRu5YTzw7gA+cCbI= X-Authority-Analysis: v=2.4 cv=F97C5ahN c=1 sm=1 tr=0 ts=6ac4afe2 cx=c_pps a=vVfyC5vLCtgYJKYeQD43oA==:117 a=nuhDOHQX5FNHPW3J6Bj6AA==:17 a=IkcTkHD0fZMA:10 a=660iZSQnnn4A:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=Um2Pa8k9VHT-vaBCBUpS:22 a=Byx-y9mGAAAA:8 a=EUspDBNiAAAA:8 a=WbzL4V9Atknj4SyEsUoA:9 a=QEXdDO2ut3YA:10 a=rl5im9kqc5Lf4LNbBjHf:22 X-Proofpoint-ORIG-GUID: 7WmY_zQq1hFN7zhob38Suk6EzZkrj0MY X-Proofpoint-GUID: 7WmY_zQq1hFN7zhob38Suk6EzZkrj0MY X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-10-06_02,2026-10-05_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 phishscore=0 clxscore=1015 impostorscore=0 malwarescore=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2610060033 On 9/29/2026 6:36 PM, Hui Su wrote: > rate_limit_us_store() is called with the governor attribute set > update_lock held, but sugov_start() updates freq_update_delay_ns from > the same tunable without taking that lock. > > This allows the two paths to interleave as follows: > > sugov_start() rate_limit_us_store() > > read old rate_limit_us > write new rate_limit_us > publish the new delay > publish the old delay > > The sysfs tunable then contains the new value while > freq_update_delay_ns contains the old one. Unlike a transient torn > read, the stale delay remains in effect until another rate limit update > or governor restart. > > Serialize sugov_start() against sysfs stores by taking the existing > governor attribute set update_lock around sugov_update_rate_limit_us(). > This keeps the fix off the scheduler hot path. > > Fixes: 9bdcb44e391d ("cpufreq: schedutil: New governor based on scheduler utilization data") The Fixes tag is accurate, but the patch cannot be cleanly backported because the code has since been refactored. > Signed-off-by: Hui Su Reviewed-by: Zhongqiu Han > --- > kernel/sched/cpufreq_schedutil.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/kernel/sched/cpufreq_schedutil.c b/kernel/sched/cpufreq_schedutil.c > index 49ccd6f1c185..e759f09be638 100644 > --- a/kernel/sched/cpufreq_schedutil.c > +++ b/kernel/sched/cpufreq_schedutil.c > @@ -861,7 +861,11 @@ static int sugov_start(struct cpufreq_policy *policy) > void (*uu)(struct update_util_data *data, u64 time, unsigned int flags); > unsigned int cpu; > > + /* Serialize against rate_limit_us_store(), which holds this lock. */ > + mutex_lock(&sg_policy->tunables->attr_set.update_lock); Nit: Better to wrap this in a helper, e.g.gov_attr_set_lock(). Besides, When I started reviewing this patch, I initially considered removing the freq_update_delay_ns cache for a lockless design. However, since it is on a hot path, doing the multiplication every time could hurt performance. > sugov_update_rate_limit_us(sg_policy); > + mutex_unlock(&sg_policy->tunables->attr_set.update_lock); > + > sg_policy->last_freq_update_time = 0; > sg_policy->next_freq = 0; > sg_policy->work_in_progress = false; > > base-commit: 63de2367f6d280904a9c5e5bbc7c75bb91c5b3d8 > -- Thx and BRs, Zhongqiu Han