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Wed, 13 May 2026 13:39:51 +0000 (GMT) Received: from li-7bb28a4c-2dab-11b2-a85c-887b5c60d769.ibm.com.com (unknown [9.39.28.2]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 13 May 2026 13:39:50 +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, pauld@redhat.com Subject: [PATCH v3 3/4] sched/fair: Add sched_smt_active check for fastpaths Date: Wed, 13 May 2026 19:09:33 +0530 Message-ID: <20260513133934.380347-4-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260513133934.380347-1-sshegde@linux.ibm.com> References: <20260513133934.380347-1-sshegde@linux.ibm.com> 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-Authority-Analysis: v=2.4 cv=Us1T8ewB c=1 sm=1 tr=0 ts=6a047f2d cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=zd2uoN0lAAAA:8 a=VnNF1IyMAAAA:8 a=BCh2IS2iSeRwy_Yvm5cA:9 X-Proofpoint-GUID: 7Q9_bEvMHnnjNPruNxKpBljIzw18s1gm X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTEzMDE0MCBTYWx0ZWRfX3s7YGd6quMPH 5Chfku1twTphqVRxIu0ZivzDdiglz+9CWPIOW/LH5T04sU5s33WWcBoUgiox3gCt9y++N5hXwfy Hipp8/7WglQNjp5FPKFJOJcZea5xt0eLUIrCn9QICrjEFmITXHhN29MlKl1Eoiq6Lu0wdG6S5TO OPgdaWR8kvqB8A6KLjaS3frA8zHBSCHnq8CnG0unsigObrK3loEqrMqVAiRPBrQsS1keSFc9zkA YXMyTMgtHuUvoUh15zytGfdbjnfD2BA0jcK2Q61gCxM+9ccYqYD3cNdWO2NjSgNOmkgqeu+frCf iQwjyQZd3A/NA0b16255KzWMQyK95aZDVtpBDm26zSL2kBLMkUeAz9XF7Ee7hvvfnND5/5oEQJb 3rJUDZyM4Lund4Vfud3LK8M6hk868Dltdb56Qa2TwZKfybvfALiogfEE8qOM1+6c1sGxs19KuO5 y6Ogku/SseNiGLJT5bA== X-Proofpoint-ORIG-GUID: x3Okb7pp8xsn0IFwHvnVTK08UtZ2Agsr 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=2026-05-13_01,2026-05-08_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 impostorscore=0 lowpriorityscore=0 bulkscore=0 suspectscore=0 spamscore=0 malwarescore=0 clxscore=1015 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605050000 definitions=main-2605130140 For fastpaths such as wakeup and load balance even minimal code additions can add up. is_core_idle is accessed during load balance. Other callsites of is_core_idle make sched_smt_active() check first. Make the same check in should_we_balance. Rest of access to cpu_smt_mask isn't in fastpath. Note: Remove the stale comment above is_core_idle. Enqueue methods of fair aren't close to it anymore. Suggested-by: K Prateek Nayak Signed-off-by: Shrikanth Hegde --- kernel/sched/fair.c | 8 +++----- 1 file changed, 3 insertions(+), 5 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 353e31ecaadc..964014a74cf9 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1578,10 +1578,7 @@ update_stats_curr_start(struct cfs_rq *cfs_rq, struct sched_entity *se) se->exec_start = rq_clock_task(rq_of(cfs_rq)); } -/************************************************** - * Scheduling class queueing methods: - */ - +/* Check sched_smt_active before calling this to avoid overheads in fastpaths */ static inline bool is_core_idle(int cpu) { int sibling; @@ -11995,7 +11992,8 @@ static int should_we_balance(struct lb_env *env) * balancing cores, but remember the first idle SMT CPU for * later consideration. Find CPU on an idle core first. */ - if (!(env->sd->flags & SD_SHARE_CPUCAPACITY) && !is_core_idle(cpu)) { + if (!(env->sd->flags & SD_SHARE_CPUCAPACITY) && + sched_smt_active() && !is_core_idle(cpu)) { if (idle_smt == -1) idle_smt = cpu; /* -- 2.47.3