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Tue, 9 Jun 2026 19:51:50 +0000 (GMT) Message-ID: Date: Wed, 10 Jun 2026 01:21:50 +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 00/20] sched: Introduce cpu_preferred_mask and steal-driven vCPU backoff To: linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, tj@kernel.org, christian.loehle@arm.com, arighi@nvidia.com, juri.lelli@redhat.com, vincent.guittot@linaro.org Cc: tglx@kernel.org, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.com, yury.norov@gmail.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, pauld@redhat.com, tommaso.cucinotta@gmail.com, maz@kernel.org, rafael@kernel.org, kprateek.nayak@amd.com, iii@linux.ibm.com References: <20260514152204.481115-1-sshegde@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260514152204.481115-1-sshegde@linux.ibm.com> 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=HppG3UTS c=1 sm=1 tr=0 ts=6a286ee4 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=MfTJy7a84anIrKwLmwEA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: tI6xHs5f3FZJM9HNMoQODekwM7su6NWb X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjA5MDE4NCBTYWx0ZWRfX6KAegjHknoeo ypgVf55Mhm7jtokdKXH4rbryW9SkAuQUuvlDxgL+s2TbzSA8NtD7zOSMYnIP+JK9QsZKYs/P9vA MwdeeFopT5tkkmj/sRyNhkKJ7c5hW6N8jSe49adDDDRGg1FlgcBqVnGTST7xykhj7FE9e9SWxV5 jhgolrhzuJfyZgBWDvWZb71he/uOWXjB8z2bl7VnKl/e4RUq3VBS9q0eZ5/EFQhFnc6yubEH1Fx goQTYT2eaXVYZxie5o30INwhxJVyDPcTpaUCdC3vssxzUNhgrKLp5uy2rXZ1PD8pRn96GVi39fk 9K5OWpLTTnmMXvwlA2CYjDLAWuUrv4472vshnuYruzVVt0Tn8UDhK/pXjl26pblcK05ROI21bnl lW0MXyBojs6Z+kiVgGTiXRWW8nwSlXDl/3K0crwDlIBDfYB356xAP2S/dOokBQAXW/jSthEKxE9 ZeiKfxkQyd29MSAnxqQ== X-Proofpoint-ORIG-GUID: xoE5vJhJufPfkegHfbKSJ4ThKSq3QjjI 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=2026-06-09_04,2026-06-09_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 adultscore=0 phishscore=0 malwarescore=0 impostorscore=0 priorityscore=1501 clxscore=1015 bulkscore=0 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605210000 definitions=main-2606090184 On 5/14/26 8:51 PM, Shrikanth Hegde wrote: > TODO/OPEN Questions: > > - SCHED_EXT is still pending. I tried adding few checks in > scx_idle_test_and_clear_cpu, pick_idle_cpu_in_node and push the > sched_ext task in tick. But it hasn't still worked with scx_simple. > I will try to figure it out. But i may need help since > I am yet wade deeper waters in sched_ext. > In addition to pushing the task out at sched_tick, Did some hacking around wake up path scx_select_cpu_dfl to make it aware of cpu_preferred state. That didn't make it work. then tried to Push the task out in enqueue_task_scx. That makes it somewhat work, but still has warning with scx_simple. Given there are many different scx_ flavours, it might make sense add a new one which is aware of preferred state and can manage it without any change to the default implementations using custom select_cpu/enqueue/dequeue etc. So I am thinking sched_ext bit will have to be pursued later as i don't have much knowledge there still. Hacked Code that was tried for scx_simple. diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 9a92a479720d..4009ca1ec027 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -11361,7 +11361,8 @@ void sched_push_current_non_preferred_cpu(struct rq *rq) /* Push only if it is FAIR/RT class */ if (push_task->sched_class != &fair_sched_class && - push_task->sched_class != &rt_sched_class) + push_task->sched_class != &rt_sched_class && + push_task->sched_class != &ext_sched_class) return; if (kthread_is_per_cpu(push_task) || diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index f5a3233ead1a..a7a87f849e03 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -2043,6 +2043,11 @@ static void enqueue_task_scx(struct rq *rq, struct task_struct *p, int core_enq_ goto out; } + if (!cpu_preferred(rq->cpu)) { + sched_push_current_non_preferred_cpu(rq); + return; + } + set_task_runnable(rq, p); p->scx.flags |= SCX_TASK_QUEUED; rq->scx.nr_running++;