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Mon, 8 Jun 2026 16:39:42 +0000 (GMT) Message-ID: Date: Mon, 8 Jun 2026 18:39:41 +0200 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 07/20] sched/fair: Select preferred CPU at wakeup when possible To: K Prateek Nayak , Shrikanth Hegde , linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com Cc: 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> <20260514152204.481115-8-sshegde@linux.ibm.com> Content-Language: en-US From: Ilya Leoshkevich 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-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjA4MDE1OCBTYWx0ZWRfXxzPi1OR2QA6B gepZd3yeJt8SgUkecY8ycDBpWLbRWB78Z1OWr+210Y3Q5PGH/ql0lyxtZViu68Ii8SqpkpNYrZ0 RDkWv6B82Ulev0vRpAImThtHmFHBQkQ+eXKbzAxcjxeFzx/0+/SBGtb/vKyZzMBOgOq+5fCXWf8 TVCi/i1vIjt418/c9egDbt8BDLr6R0Vo43jGat5lvWpifnsoyuSg10tLFrQQvwW6xfBLwwoIcbl ykVTIDIPBiP7BXrbZHyfSrbUzUzINOhLIUTwpx62JQThlzCNgVEB76atYELqYSqtI4nUMK4dUvB w8+KxNNHo3Qwea53+QiXkDnKfMTaxgwAvLxJy3z26yd0EUSVX9O64gypeprq1bnDXs/JVPITGZ6 vDxGi4ENbzLzdGv5tx3j+U2X0Fpb5TnCFpOtTDIOzWnLaPdqmHLHSaFCiEh+C1I1vrS3iQAFxI7 X4pANxqXLbi5WMfiCiQ== X-Authority-Analysis: v=2.4 cv=QKhYgALL c=1 sm=1 tr=0 ts=6a26f055 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=OFr9xA4t93nzt8PCQZwA:9 a=QEXdDO2ut3YA:10 a=O8hF6Hzn-FEA:10 X-Proofpoint-GUID: 5vvCZ1vO7A0mw2qKz5c_AgB64WFGZm0m X-Proofpoint-ORIG-GUID: qnzVjMeXUdonGntV9qdV3GKJ7zEIf0nI 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=2026-06-08_04,2026-06-05_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 lowpriorityscore=0 bulkscore=0 adultscore=0 phishscore=0 malwarescore=0 impostorscore=0 suspectscore=0 spamscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605210000 definitions=main-2606080158 On 6/4/26 07:14, K Prateek Nayak wrote: > Hello Shrikanth, > >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 29fbb5287cfc..a704285ac55a 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -7743,7 +7743,8 @@ static inline int sched_balance_find_dst_cpu(struct sched_domain *sd, struct tas >> { >> int new_cpu = cpu; >> >> - if (!cpumask_intersects(sched_domain_span(sd), p->cpus_ptr)) >> + if (!cpumask_intersects(sched_domain_span(sd), p->cpus_ptr) && > > Doesn't this mean we have no CPUs in this sd that fits the affinity > requirements? > >> + cpu_preferred(prev_cpu)) > > There is no point in going down the function if the affinity constraints > aren't met since we are traversing the hierarchy top-down and none of > the groups / child domains will satisfy the affinity requirements. > > Since the CPU returned here is again checked for is_cpu_allowed(), we'll > eventually hit the select_fallback_rq() path anyways so the check for > cpu_preferred(prev_cpu) seems unnecessary unless I'm missing something. Do we need to add is_cpu_allowed() check to sched_exec()? Or is the existing cpu_active() check enough? > >> return prev_cpu; >> >> /* >