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Mon, 23 Mar 2026 19:36:51 +0000 (GMT) From: Shrikanth Hegde To: mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, tglx@kernel.org, frederic@kernel.org, anna-maria@linutronix.de, linux-kernel@vger.kernel.org Cc: sshegde@linux.ibm.com, kprateek.nayak@amd.com, juri.lelli@redhat.com, vschneid@redhat.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, mkchauras@gmail.com Subject: [PATCH 1/4] sched/fair: get this cpu once in find_new_ilb Date: Tue, 24 Mar 2026 01:06:27 +0530 Message-ID: <20260323193630.640311-2-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260323193630.640311-1-sshegde@linux.ibm.com> References: <20260323193630.640311-1-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: quoted-printable X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: j-7IkSL2Aazp0rYg72iVsMEk-xW20TW0 X-Authority-Analysis: v=2.4 cv=aMr9aL9m c=1 sm=1 tr=0 ts=69c19659 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=pGLkceISAAAA:8 a=zd2uoN0lAAAA:8 a=xKVtjyDvgW7pnAdJ2ZUA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzIzMDE0MyBTYWx0ZWRfX8lDq6Olv+YRy WAhoswSTlvbDl0FajmmPw1vx12KIrTfRBJ7RHwMN9RyoKXoju4IAsNtoO8IbliwTu/Mf//HUrlh BHTOAiHN6kSO1lY2/4u9CFCv6ytezoph0UcTiz0o520sS5z1OeBa66l+ZLjCV4gdvrebi5ZLiYJ ZF+oZOxqc6MFWmdMYNy9WDaPi5pBI/4iEXjIVIgbRjgVheA2Vvajsal2HnbP1FRl41w1qkNnG7K s+pEUW/VzjGbUqOHxsfeUD93U3rEGdpVCkOJOb6yxuwRh7lzn0lcRnuQk90coJ0hHzjmt1lLS+5 HG78Xt/lt8WDlO4Ns9IsEVV0X0WSlEQA+QHzDRnof0Fmomyx3y980qlPPgFE8fdBlLPvDLFdHfN E4WGaQ8qrvcwLA8SikbCNpCQYWi9uVzN0/xDmgMyBK+Yi1R0qomg7FmvH8x3xWFdy5aeOUOuGB3 eo9uXhwq/SfROdPAasA== X-Proofpoint-GUID: 39C_Qrf15ihGMhc6NROA7LXg_lKrrMhy 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=2026-03-23_04,2026-03-23_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 lowpriorityscore=0 adultscore=0 impostorscore=0 malwarescore=0 suspectscore=0 phishscore=0 priorityscore=1501 bulkscore=0 clxscore=1015 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2603050001 definitions=main-2603230143 Content-Type: text/plain; charset="utf-8" Calling smp_processor_id() on: - In CONFIG_DEBUG_PREEMPT=3Dy, if preemption/irq is disabled, then it does not print any warning. - In CONFIG_DEBUG_PREEMPT=3Dn, it doesn't do anything apart from getting __smp_processor_id So with both CONFIG_DEBUG_PREEMPT=3Dy/n, in preemption disabled section it is better to cache the value. It could save a few cycles. Though tiny, repeated in loop could add up to a small value. find_new_ilb is called in interrupt context. So preemption is disabled. So Hoist the this_cpu out of loop Reviewed-by: Mukesh Kumar Chaurasiya (IBM) Reviewed-by: K Prateek Nayak Signed-off-by: Shrikanth Hegde --- Split it from v1 and found a few more places. Rest of the bits of v1 is worked out separate v1: https://lore.kernel.org/all/20260319065314.343932-1-sshegde@linux.ibm.c= om/ kernel/sched/fair.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 1b62cb68faae..9298f49f842c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -12626,14 +12626,14 @@ static inline int on_null_domain(struct rq *rq) */ static inline int find_new_ilb(void) { + int this_cpu =3D smp_processor_id(); const struct cpumask *hk_mask; int ilb_cpu; =20 hk_mask =3D housekeeping_cpumask(HK_TYPE_KERNEL_NOISE); =20 for_each_cpu_and(ilb_cpu, nohz.idle_cpus_mask, hk_mask) { - - if (ilb_cpu =3D=3D smp_processor_id()) + if (ilb_cpu =3D=3D this_cpu) continue; =20 if (idle_cpu(ilb_cpu)) --=20 2.47.3