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Fri, 26 Jun 2026 13:17:24 +0000 (GMT) Received: from [9.39.23.71] (unknown [9.39.23.71]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 26 Jun 2026 13:17:24 +0000 (GMT) Message-ID: <6c567674-231a-4d21-b9e8-e9c4b23cfadc@linux.ibm.com> Date: Fri, 26 Jun 2026 18:47:23 +0530 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 07/24] sched/fair: Select preferred CPU at wakeup when possible 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, corbet@lwn.net, 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, 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, rdunlap@infradead.org, kernellwp@gmail.com, linux-doc@vger.kernel.org References: <20260625124648.802832-1-sshegde@linux.ibm.com> <20260625124648.802832-8-sshegde@linux.ibm.com> <20260626095948.GO1181229@noisy.programming.kicks-ass.net> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260626095948.GO1181229@noisy.programming.kicks-ass.net> 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=X4Ni7mTe c=1 sm=1 tr=0 ts=6a3e7bf2 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=UWYZ6Kb2ZmTN1TUfP5sA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwNjI2MDEwNSBTYWx0ZWRfX+N6T0A4C4d2l 0ZhdK8IeUMKUOb+5yLncOSzrTQ/CYR7D6bzd9aHlPb8mxon4Seb8ed82TYSk/7w2ss4zTFNl6Xd Cco/D/FAFSVfJvyKDwvuv3tWU5NFhCQ= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjI2MDEwNSBTYWx0ZWRfXxKbU5diXehQ4 4OfC40uv9UL6mt8o5of0zaOLGMmk7Z+i0GZCic5uQ4VZ9IEVQYrp8nmlWOn1llGBcn4MLBAYl0a I2Vs6L8z2t/oqibxj+Zi6J2cjb0pkCK160mQMKAmYsc5NWkPyiAWsplsWW2hFuZmqRgm0gg36Qb JRFF53il7WUd+0GfQXjJqi8cvLrJXdCLB1x0PvJbpLmr5/VnwihvOe5IUQx9Vo6PlOIZM5KtUeE hKCf6meFD7Sg/IXYlqCs6lCOqxJ5WrwbYEHVi/8JQuqeG0DvJe9OxfBPFg2C0FkUl7qBgBxS6CB qFWOkWvG/wtVEiFijYh2LU1wG2jXO9wSC2DNmfSaiWLFULE35Md8b1jcL1AbO68FC9fJVh60JuB xC2qeeSrPdGU3vlEtO+GaZJPb2dm4yCUffD8uCRPP5/rKp7vZYzg9pscI3YVU+eFq39S8UiYGEH 3aciaNvTlH0XAdoe3LQ== X-Proofpoint-ORIG-GUID: -APv6aMC4ZRF0Ipsr8gugyQEWrIUdsBe X-Proofpoint-GUID: 15ngkTwNt-c-U_o-oR0ka27BYY-lU4BQ 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=2026-06-26_03,2026-06-24_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 bulkscore=0 suspectscore=0 spamscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 clxscore=1015 adultscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2606260105 Hi Peter, Thank you very much for going through the patches. On 6/26/26 3:29 PM, Peter Zijlstra wrote: > On Thu, Jun 25, 2026 at 06:16:31PM +0530, Shrikanth Hegde wrote: >> Update available_idle_cpu to consider preferred CPUs. This takes care of >> lot of decisions at wakeup to use only preferred CPUs. There is no need to >> put those explicit checks everywhere. >> >> Signed-off-by: Shrikanth Hegde >> --- >> kernel/sched/sched.h | 3 +++ >> 1 file changed, 3 insertions(+) >> >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >> index 5d009c2529b2..148fe6145f1a 100644 >> --- a/kernel/sched/sched.h >> +++ b/kernel/sched/sched.h >> @@ -1434,6 +1434,9 @@ static inline bool available_idle_cpu(int cpu) >> if (!idle_rq(cpu_rq(cpu))) >> return 0; >> >> + if (!cpu_preferred(cpu)) >> + return 0; >> + >> if (vcpu_is_preempted(cpu)) >> return 0; >> > > This one might hurt, it is a whole extra cacheline in otherwise already > sensitive (wakeup) paths. > Yes, this could be costly. If wakeup returns a non-preferred CPU, is_cpu_allowed would catch it. So, i think we can avoid repeated computation of it in available_idle_cpu. Let me see if removing it still achieves the functionality of moving out fast enough and numbers are close enough to with it.