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Tue, 28 Oct 2025 11:42:11 GMT Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 861CB20043; Tue, 28 Oct 2025 11:42:11 +0000 (GMT) Received: from smtpav03.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AEFF720040; Tue, 28 Oct 2025 11:42:08 +0000 (GMT) Received: from linux.ibm.com (unknown [9.126.150.29]) by smtpav03.fra02v.mail.ibm.com (Postfix) with SMTP; Tue, 28 Oct 2025 11:42:08 +0000 (GMT) Date: Tue, 28 Oct 2025 17:12:07 +0530 From: Srikar Dronamraju To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Michael Ellerman , Madhavan Srinivasan , linuxppc-dev@lists.ozlabs.org, Ben Segall , Christophe Leroy , Dietmar Eggemann , Ingo Molnar , Juri Lelli , Mel Gorman , Nicholas Piggin , Steven Rostedt , Thomas Gleixner , Valentin Schneider , Vincent Guittot Subject: Re: [PATCH 1/2] sched: Feature to decide if steal should update CPU capacity Message-ID: Reply-To: Srikar Dronamraju References: <20251028104255.1892485-1-srikar@linux.ibm.com> <20251028111813.GK3245006@noisy.programming.kicks-ass.net> 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=iso-8859-1 Content-Disposition: inline In-Reply-To: <20251028111813.GK3245006@noisy.programming.kicks-ass.net> X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMDI1MDAxOSBTYWx0ZWRfX3E65AGWX3YDK ZcQMHwei5KhTLQIaIVtiDqwCXhZbu1FjPJQtDXYSxAYBUjt5ze1UrTdq4dEtGDZOpc8UYjEsZcw X7ZmLTRjfQZZRUJiYwViBDKZUAiMH1VfPQ1d2gWW6ws92nvgNi8LOyTLouC1y/UDiictDsCJdKZ kbVahpA3tpLiqzrV23mzldrF/XGPLaaNXfxvJvRVIvKbnIjct49HVkcH1Sb4RzAXaE9jN6MoRpb Mvo+IKDRH1o1ZOLazf655vXeEc3jhLy1V9L4t4fcgrXPe0rbu5MY+2d5Lw/ZKsPE/EzxWta/Clf DKq7AIi/kBg03+IsQ08kcGkSn2gTxH+f16YdzKhKOVDEA6Qc7UCp/jtnHc/VRmbzprTsg/cSyDb Iqrs6gwNJnv+xsVV5STLhoIR2WxaUQ== X-Proofpoint-GUID: 7EE3qoUTsocvgzt5-oWxn5mEHfSh58gl X-Authority-Analysis: v=2.4 cv=V8ZwEOni c=1 sm=1 tr=0 ts=6900ac19 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=8nJEP1OIZ-IA:10 a=x6icFKpwvdMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=JfrnYn6hAAAA:8 a=an05pmTB2Cu0hgrGQSoA:9 a=wPNLvfGTeEIA:10 a=1CNFftbPRP8L7MoqJWF3:22 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-ORIG-GUID: vIm5uMRFkyLB3neSmqeFXK9ByuhWRcRx X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-10-28_04,2025-10-22_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 phishscore=0 lowpriorityscore=0 malwarescore=0 adultscore=0 bulkscore=0 spamscore=0 clxscore=1015 suspectscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510020000 definitions=main-2510250019 * Peter Zijlstra [2025-10-28 12:18:13]: > On Tue, Oct 28, 2025 at 04:12:54PM +0530, Srikar Dronamraju wrote: > > At present, scheduler scales CPU capacity for fair tasks based on time > > spent on irq and steal time. If a CPU sees irq or steal time, its > > capacity for fair tasks decreases causing tasks to migrate to other CPU > > that are not affected by irq and steal time. All of this is gated by > > NONTASK_CAPACITY. > > > > In virtualized setups, a CPU that reports steal time (time taken by the > > hypervisor) can cause tasks to migrate unnecessarily to sibling CPUs that > > appear to be less busy, only for the situation to reverse shortly. > > > > To mitigate this ping-pong behaviour, this change introduces a new > > scheduler feature flag: ACCT_STEAL which will control whether steal time > > contributes to non-task capacity adjustments (used for fair scheduling). > > Please don't use sched_feat like this. If this is something that wants > to be set by architectures move it to a normal static_branch (like eg. > sched_energy_present, sched_asymc_cpucapacity, sched_cluster_active, > sched_smt_present, sched_numa_balancing etc.). Ok, Peter, will move it to a static_branch approach and post a v2. -- Thanks and Regards Srikar Dronamraju