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Mon, 1 Dec 2025 18:32:07 +0000 (GMT) From: Shrikanth Hegde To: mingo@kernel.org, peterz@infradead.org, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, kprateek.nayak@amd.com Cc: sshegde@linux.ibm.com, dietmar.eggemann@arm.com, vschneid@redhat.com, rostedt@goodmis.org, tglx@linutronix.de, tim.c.chen@linux.intel.com Subject: [PATCH 2/4] sched/fair: Change likelyhood of nohz nr_cpus check Date: Tue, 2 Dec 2025 00:01:44 +0530 Message-ID: <20251201183146.74443-3-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251201183146.74443-1-sshegde@linux.ibm.com> References: <20251201183146.74443-1-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-Spam-Details-Enc: AW1haW4tMjUxMTI5MDAwMCBTYWx0ZWRfX8SsTJDvUbncm Opc1DOjqjMJXiqrE4NBT1YStlbPylkXHzyALwR0p0YYvZUJKxBizGXl9fcoiqBFR3bb+rfPVaEB 8yMQH/qoUVG0kTW/rtSMThBM+1TLAtwQt8M+fdol7vyQMN/+yVsN8hhZoyuKRBuL/haJb2dYr3N TuuN8l4Sb93LlCW37YSOrHU6MaHgaWdnlZRx37Z1okPvIxL6adV/JsgvATezw5RIlbc4ZV3PoJQ g4htXluGk+wk/OLSAd31t3qjRTKVIyB50wyT4pkHOZYMYx6uYWQLli1ded2J6fQhEtMgakMzL+6 /HN+XP7yiBV1shro+OymdKnPkORXfVy16KPlvy+rp3KEfXcE57ujpuNOLQHcHBwHjhAF+8nCVJi FD+hMi0lwLzTU8/Wgq0IHnJFsZ+bdA== X-Authority-Analysis: v=2.4 cv=dIerWeZb c=1 sm=1 tr=0 ts=692ddf2d cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=wP3pNCr1ah4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=L2DUigS4eapgOTKWHN4A:9 X-Proofpoint-ORIG-GUID: HgD4PhUwfn7ec9YrsPVcelZ3hYtxdLRR X-Proofpoint-GUID: HgD4PhUwfn7ec9YrsPVcelZ3hYtxdLRR X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-28_08,2025-11-27_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 lowpriorityscore=0 clxscore=1015 spamscore=0 malwarescore=0 suspectscore=0 adultscore=0 bulkscore=0 impostorscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511290000 Content-Type: text/plain; charset="utf-8" These days most of the system have multi cores. The likelyhood of at least one or more CPUs in nohz (idle state) is higher. So move likely to unlikely. Allow stats balancing to complete when there are no nr_cpus as the check happens later. Current code might race and may not set nohz.has_blocked =3D 0 even when nohz.nr_cpus =3D=3D 0 Signed-off-by: Shrikanth Hegde --- kernel/sched/fair.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 61cc3fdfa45b..55746274af06 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -12448,10 +12448,10 @@ static void nohz_balancer_kick(struct rq *rq) goto out; /* * None are in tickless mode and hence no need for NOHZ idle load - * balancing: + * balancing, do stats update if its due */ - if (likely(!atomic_read(&nohz.nr_cpus))) - return; + if (unlikely(!atomic_read(&nohz.nr_cpus))) + goto out; =20 if (rq->nr_running >=3D 2) { flags =3D NOHZ_STATS_KICK | NOHZ_BALANCE_KICK; --=20 2.43.0