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15.20.9769.016; Fri, 3 Apr 2026 17:07:46 +0000 From: "Ionut Nechita (Wind River)" To: rafael@kernel.org Cc: aboorvad@linux.ibm.com, christian.loehle@arm.com, dsmythies@telus.net, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, sunlightlinux@gmail.com Subject: Re: [PATCH v2 1/2] cpuidle: governors: menu: Refine stopped tick handling Date: Fri, 3 Apr 2026 20:07:22 +0300 Message-ID: <20260403170722.575573-1-ionut.nechita@windriver.com> X-Mailer: git-send-email 2.43.0 In-Reply-To: <3341782.5fSG56mABF@rafael.j.wysocki> References: <3341782.5fSG56mABF@rafael.j.wysocki> Content-Transfer-Encoding: 8bit Content-Type: text/plain X-ClientProxiedBy: VI4PEPF0000012E.AUTP296.PROD.OUTLOOK.COM (2603:10a6:808:1::8ad) To SJ2PR11MB7546.namprd11.prod.outlook.com (2603:10b6:a03:4cc::8) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: 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a=bi6dqmuHe4P4UrxVR6um:22 a=HK-ge7EqtdluswH-FwHe:22 a=pGLkceISAAAA:8 a=NTM3MBKb6arpASKX1lgA:9 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=2026-04-03_05,2026-04-03_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 spamscore=0 adultscore=0 clxscore=1011 impostorscore=0 malwarescore=0 bulkscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2604030153 On Mon, 23 Feb 2026 16:38:55 +0100, Rafael J. Wysocki wrote: > Update the menu governor in accordance with the above and use twice > the tick period length as the "safe timer range" for allowing the > original predicted_ns value to be used even if the tick has been > stopped. Tested this on 6.12.79-rt17 with isolated CPUs (nohz_full=1-16, isolcpus=nohz,domain,managed_irq,1-16) on Intel Xeon Gold 6338N. cyclictest --priority 95 --nsecs --duration 600 --affinity 1-15 --threads 15 --mainaffinity 0 Before (6.12.79-rt17 without patch): Avg: ~1780ns, Max T:3-T:8: 9300-9700ns After (6.12.79-rt17 + this patch): Avg: ~1790ns, Max T:3-T:14: 5200-6100ns The patch reduces worst-case latency on threads T:3-T:14 from ~9500ns to ~5800ns on isolated CPUs with nohz_full. T:0-T:2 still show occasional higher spikes (9400-10700ns) but the overall tail latency improvement is clear. Tested-by: Ionut Nechita