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Wed, 10 Jun 2026 17:13:25 +0000 (GMT) Received: from [9.124.212.124] (unknown [9.124.212.124]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 10 Jun 2026 17:13:25 +0000 (GMT) Message-ID: <476fa19d-d5fb-4ac5-8363-607bdc02da86@linux.ibm.com> Date: Wed, 10 Jun 2026 22:43:24 +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 v3 09/20] sched/rt: Select a preferred CPU for wakeup and pulling rt task From: Shrikanth Hegde To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, kprateek.nayak@amd.com, iii@linux.ibm.com, tglx@kernel.org, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, mgorman@suse.de, bsegall@google.com, maddy@linux.ibm.com, srikar@linux.ibm.com, hdanton@sina.com, chleroy@kernel.org, vineeth@bitbyteword.org, frederic@kernel.org, arighi@nvidia.com, pauld@redhat.com, christian.loehle@arm.com, tj@kernel.org, tommaso.cucinotta@gmail.com, maz@kernel.org, rafael@kernel.org References: <20260514152204.481115-1-sshegde@linux.ibm.com> <20260514152204.481115-10-sshegde@linux.ibm.com> <20260609112505.GC48970@noisy.programming.kicks-ass.net> Content-Language: en-US In-Reply-To: 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-Authority-Analysis: v=2.4 cv=b4uCJNGx c=1 sm=1 tr=0 ts=6a299b43 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=Rw7tGMVdhmuCcHwccy8A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: 9IgEefhFB-PlYYZOEKaCJGIFpr6BRPqX X-Proofpoint-GUID: psyLZIBfR1JRvPgl5ufNPjpezfbgbC7g X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjEwMDE2MSBTYWx0ZWRfX7F+jzb3uqlC0 u1W0wLpsUWShLwJR4xOuSDaC7fFS5zfODCFdl7Tzm8SuWSZ5S/IO63YvLRF28I7BJXI7UrqnA13 7c/UyZ2lXOnCHLB6u38DkW3+MNtS6OUS7LIC3nKfcVIJPQPONkBmh33J9It30mC5jTjpGiEnk6R bvUSivHgnu2LTOA9t+bCGXeQTsmQR3SzHZ+E0YK+6AIkrlEkIh3yUTMeInYzzX/7KJ5Qzm41tYH OhDg3wThHIX0uHP4agaYPYrbGr+YruwqC0wNp9JJ7OGEVlLr2IFaG5jrNE1WxaXnBze5uLS9PED FnHdWg7Dx/PjHZfrwiQq5SwTUqcbU1oMJWHsbEqdQPK+4M7O5MVN//W2WAwEO72sHuUoQkes5gz 8rKt55JFjzDYr49s+j8NwLX27m/HfaWUgRT3pHf/h/TkZMKi+XZJVmDi/5QOsTCGlKitesBEO0g 1PPNgulAaxm0Lxv2Bqg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-10_03,2026-06-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 spamscore=0 bulkscore=0 phishscore=0 priorityscore=1501 lowpriorityscore=0 adultscore=0 malwarescore=0 impostorscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605210000 definitions=main-2606100161 Hi Peter. On 6/9/26 5:00 PM, Shrikanth Hegde wrote: > Hi Peter. Thanks for taking a look at the patches. > > On 6/9/26 4:55 PM, Peter Zijlstra wrote: >> On Thu, May 14, 2026 at 08:51:53PM +0530, Shrikanth Hegde wrote: >>> For RT class, >>> - During wakeup choose a preferred CPU. >>> - For push_rt framework, limit pushing to preferred CPUs >>> - Pull the rt task only if CPU is preferred. >> >> So this one might have the potential to break things. Preferring a >> preferred cpu, sure, but to the exclusion of active, perhaps not. >> > > I don't think we are excluding active. > I thought a bit more. On most common workloads, rt is likely not dominant/significant in VM environments. I am thinking to drop rt changes in the next version. If we see a need for it, then that support could be added. I reverted these changes and ran real life workload (daytrader) mentioned in the cover-letter and I don't see its impact. >> Also, where are the DL changes? > > DL changes are not there. The reason being on such systems running DL > tasks will not make sense as timelines are subjected to vCPU preemption > and there is no easy way to force run a vCPU. > > RT is not a primary use case too. But have seen a few workload spawn RT > tasks today. So it is there. > So, initial support will be for FAIR only. Other class support could be brought based on the use-case. Does that make sense?