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Fri, 15 May 2026 17:25:12 +0000 (GMT) Received: from li-7bb28a4c-2dab-11b2-a85c-887b5c60d769.ibm.com.com (unknown [9.39.30.78]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 15 May 2026 17:25:11 +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 v4 3/4] sched/fair: Add sched_smt_active check for fastpaths Date: Fri, 15 May 2026 22:54:55 +0530 Message-ID: <20260515172456.542799-4-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260515172456.542799-1-sshegde@linux.ibm.com> References: <20260515172456.542799-1-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-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTE1MDE3NSBTYWx0ZWRfX5stfIcU5FqRE 6DrhvaydWznEISvfZFB9aC61bzr/6H5Hpb5rjSTgpJb0bNlpxYs7zrXIvnefUvQmY/aupwgVAFD +bowl92IKO0tvHY/VwBLNyTIYy+oG7tY9JQdkbKgnMJQCp/6ANLTHGt6ryTwKuLjJg06o6UtYz7 p/pdOSaiK3T/FUew8EECS1wyzLXBmDYp0XYR/xP18IP3JUaQN0MWAiSwRE9IBfM42ffCYCVOyom kt1eBeI2fuKR9x8lKxkQxlgAKEN7dZJLDAnBE2h33O3DsrEmGgtCkzj3hxJ1n81vUMG1GGcRzES ztDCAEpjxQn7JTeiMJQAhGKL9E2i36KPAHAV7sBKhf2BSs3hP7N72FvXTyXqyPi6oy3uTWEyLvt HEDOQCx1cJN1CIx2GKOUBpxe3oCjnRM3p/iYiVyJ1hdVCKF7dlRDGk2zVhcbrBjfRf591huv095 0RPmP07mLnKhTNBqPJg== X-Proofpoint-ORIG-GUID: OITuhTylAV5U2y-DojEenlWApAZNrRyO X-Authority-Analysis: v=2.4 cv=aNnAb79m c=1 sm=1 tr=0 ts=6a0756fe cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==: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: H8huClDVbKXyvPukxU7-kcyrHsPuO0sV 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=2026-05-15_04,2026-05-15_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 malwarescore=0 suspectscore=0 spamscore=0 lowpriorityscore=0 impostorscore=0 priorityscore=1501 clxscore=1015 adultscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605130000 definitions=main-2605150175 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 | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 353e31ecaadc..c0d66a10d01e 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 +11992,9 @@ 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 (sched_smt_active() && + !(env->sd->flags & SD_SHARE_CPUCAPACITY) && + !is_core_idle(cpu)) { if (idle_smt == -1) idle_smt = cpu; /* -- 2.47.3