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Tue, 12 May 2026 15:21:32 +0000 (GMT) Received: from li-7bb28a4c-2dab-11b2-a85c-887b5c60d769.ibm.com.com (unknown [9.39.28.106]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 12 May 2026 15:21:31 +0000 (GMT) From: Shrikanth Hegde To: mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org Cc: sshegde@linux.ibm.com, kprateek.nayak@amd.com, juri.lelli@redhat.com, vschneid@redhat.com, dietmar.eggemann@arm.com, tj@kernel.org, rostedt@goodmis.org, mgorman@suse.de, bsegall@google.com, arighi@nvidia.com Subject: [PATCH v2 0/3] sched: Simplify ifdeffery around CONFIG_SCHED_SMT Date: Tue, 12 May 2026 20:51:22 +0530 Message-ID: <20260512152125.308280-1-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTEyMDE1OCBTYWx0ZWRfX0ScZz7V6M5ru 7t1giF22JKWaQ8CitJZ4ts0ya8Dt2U4MnpmjfdLedGp54WvqlCNeHvzwsTtuv35snqfBzZWjZ3V tc4AAlHmGXqOHk2y5iNAaWLUvjd+B5yzOcYpTqMM6pDujehahfgBWDqJdm1qMOu6Ak20E5frWwF ytdPdsKnJsg63tZ865oPbfpeodemj8Y4thJX7UZlfAn71HAk4N1yMSsGHnDTkJtnEAM69/lcKOS WadQPC/G3FTGl1qdDuTLhq0N7FNuoY9MyNK6u3AOF2E2RXBBZsBCtx1X2W1mkJyHbVC3i+1YaQG Bhm9gHwwN/+PVHuR1kW3hSIjdYOQ2NnFqLSAQCMSINe739LsdaTubSEiaKG2l8VAhqmH0a4t1oX rONspxc4rfCunwmr+YOSZQ6xoz3UiZFG/EqyzUonfAkPjOnphqPDx+F7vCqtKrrNsAl/B0F+oPM F53qPX2tYggffY7WfMg== X-Proofpoint-ORIG-GUID: JwnYVTrhkPWs6Tb3HkX9k37mlFA80vsv X-Authority-Analysis: v=2.4 cv=Jc6Ma0KV c=1 sm=1 tr=0 ts=6a034583 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=Wwc3nvnJSY7snL3-UNIA:9 X-Proofpoint-GUID: 1JLRwZZGKAvxylAv5cKrx4yzdXjS1tt1 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-11_05,2026-05-08_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 priorityscore=1501 malwarescore=0 bulkscore=0 clxscore=1015 phishscore=0 adultscore=0 lowpriorityscore=0 suspectscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605050000 definitions=main-2605120158 Semantics ========= - For CONFIG_SCHED_SMT=y: No functional change. - For CONFIG_SCHED_SMT=n: - cpu_smt_mask(cpu) becomes cpumask_of(cpu), effectively making it per CPU with no siblings. - sched_smt_present remains defined, but never becomes active: Since cpumask_weight(cpumask_of(cpu)) == 1 Performance impact ================== - CONFIG_SCHED_SMT=y: No change in generated code. - CONFIG_SCHED_SMT=n: - Small increase in text size (~0.01%) due to removal of compile-time stubs. Most paths remain effectively dead due to static keys. - Fast paths are protected using IS_ENABLED(CONFIG_SCHED_SMT). With that, cpu_smt_mask() to be used unconditionally and reduces CONFIG_SCHED_SMT-specific code paths, improving readability and maintainability. This leaves the remaining use of CONFIG_SCHED_SMT mainly for topology handling bits. Since v1[1]: - Dropped changes for stop_core_cpuslocked. intel_ifs is the only user and it gets compiled with SCHED_SMT always. Added comments around it why ifdefs are still being kept. - Decided not to add sched_smt_active checks for sched_core_cpu_deactivate and sched_core_cpu_starting, they bail out if weight(smt_mask) == 1. Hence core_lock won't be held for long. It is not fastpath either. - Thanks to Valentin Schneider and Tejun Heo for checking out the series and the feedback. Shrikanth Hegde (3): topology: Introduce cpu_smt_mask for CONFIG_SCHED_SMT=n sched: Simplify ifdeffery around cpu_smt_mask sched/fair: Add compile time check in fastpaths for CONFIG_SCHED_SMT=n include/linux/sched/smt.h | 4 ---- include/linux/topology.h | 15 +++++++++++++- kernel/sched/core.c | 6 ------ kernel/sched/ext_idle.c | 6 ------ kernel/sched/fair.c | 41 +++++---------------------------------- kernel/sched/sched.h | 6 ------ kernel/sched/topology.c | 2 -- kernel/stop_machine.c | 5 +++++ kernel/workqueue.c | 4 ---- 9 files changed, 24 insertions(+), 65 deletions(-) -- 2.47.3