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Wed, 18 Mar 2026 06:30:59 +0000 (GMT) Message-ID: Date: Wed, 18 Mar 2026 12:00:58 +0530 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] sched/core: initialize resched_latency in sched_tick() To: Steven Rostedt , Peter Zijlstra , Joseph Salisbury , Ingo Molnar Cc: Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Valentin Schneider , linux-kernel@vger.kernel.org References: <20260317195807.98850-1-joseph.salisbury@oracle.com> <20260317170943.44c41263@gandalf.local.home> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: <20260317170943.44c41263@gandalf.local.home> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: yt7N-lsVzzujE-TpsqfquqBdBr4HDJNq X-Proofpoint-GUID: 4QJmJkW-LgwR2845shp-2UrWEbqRhxJM X-Authority-Analysis: v=2.4 cv=KYnfcAYD c=1 sm=1 tr=0 ts=69ba46a9 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=meVymXHHAAAA:8 a=hK7ctBUTJFspRESFitcA:9 a=QEXdDO2ut3YA:10 a=2JgSa4NbpEOStq-L5dxp:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzE4MDA1MSBTYWx0ZWRfX1/bWFaYzPJSp L01wEN67120ZfddGvffYPci/kGYTD6xvCjAOuyURBo0x6ec3Dy+nMUWe/sXPXxRx3kGaKnbfYON TTTIE3coe9WHbbAnjICbdK2Lpw+M4B/CRiVz87QmhADbi0sDJoGVjrF3g/5HrrlOn9ymqbBKuXb +ONQwprgnLF2FBlcod7sHSrhN+8QvWWAQCnAhHdIm+As0avmV7o352jd41K/fiBrxs+KCDMMrk/ nDr8C52Q1bWrV9EsakPgkgBhXjs1JawpFkgZ/OoFWElsCntiv46nCcEkYFlYjLD0VKHSbkUMYJT YLeoZy9boodHOhYEpk+DSE1Gvd4q5+6ugoOFyWhStLPAiULQEE9w/iZH027JMOml53MhaP+reI6 Fy8OZab9QyA3OdmJtv6ol/liVau1/mXymbtd8DL73zwfOEbEZ5n0WpNVdxm7mNJUkctXWdPqIk3 9n1A/hnHDasL2ZkGJwQ== 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=2026-03-17_05,2026-03-17_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 suspectscore=0 bulkscore=0 spamscore=0 impostorscore=0 malwarescore=0 adultscore=0 clxscore=1011 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603180051 Hi. > > The code has: > > if (sched_feat(LATENCY_WARN)) > resched_latency = cpu_resched_latency(rq); > calc_global_load_tick(rq); > sched_core_tick(rq); > scx_tick(rq); > > rq_unlock(rq, &rf); > > if (sched_feat(LATENCY_WARN) && resched_latency) > resched_latency_warn(cpu, resched_latency); > > > I guess if LATENCY_WARN gets enabled between the first check and the > second, then the resched_latency could be uninitialized. > > Heck, probably could even get rid of the second sched_feat(LATENCY_WARN), > and make it simply: > > if (resched_latency) > > Reviewed-by: Steven Rostedt (Google) > > -- Steve Whats the relevance of resched_latency warnings in the age of preempt kernels being the default for majority of the archs. In case of full/lazy preemption, at the end of sched_tick itself we would call schedule if need_resched is set provided it was preemptible. It kind of makes sense for non preemptive kernels. But we have preemptoff and preemptirqoff tracers which one could use. (although may need a kernel build) What bugs is it catching these days?