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Fri, 9 Jan 2026 15:14:18 +0000 (GMT) Message-ID: <4b8e64ef-8f7c-4978-91f3-a23bab109cc5@linux.ibm.com> Date: Fri, 9 Jan 2026 20:44:18 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] sched/fair: Move checking for nohz cpus after time check To: Peter Zijlstra Cc: mingo@kernel.org, vincent.guittot@linaro.org, linux-kernel@vger.kernel.org, kprateek.nayak@amd.com, juri.lelli@redhat.com, vschneid@redhat.com, tglx@linutronix.de, dietmar.eggemann@arm.com, anna-maria@linutronix.de, frederic@kernel.org, wangyang.guo@intel.com References: <20260107065125.669668-1-sshegde@linux.ibm.com> <20260107065125.669668-2-sshegde@linux.ibm.com> <20260108124443.GA2490257@noisy.programming.kicks-ass.net> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260108124443.GA2490257@noisy.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=aaJsXBot c=1 sm=1 tr=0 ts=69611b50 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=6a8HKdklIcWgD42G3ToA:9 a=QEXdDO2ut3YA:10 a=zZCYzV9kfG8A:10 X-Proofpoint-GUID: oDCgxW0rhETp0NMjqCJ-xwzLIY_Q6GnF X-Proofpoint-ORIG-GUID: oDCgxW0rhETp0NMjqCJ-xwzLIY_Q6GnF X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTA5MDExMCBTYWx0ZWRfX/ak9fZWvbQsU tJu8OBanWbPXJaCQDDgDh7T2an6v3aWSnWzUvGQO/o4q8lk9QsUddZ4Gsu7x38ZzreEptAvcqU4 OpLrpauwTcM6n4cDcDT0YLMnSaG/CMhVbe9g7eRhPDBkFtjHWJ/gBExqkFVXQz5J4/jG2ZO095z 0A2Yz8iYBSVfUSM2bpNggO3aValesO0SS+ghgRi7t0wV1TV6DoYkFAjfsx6PaYaquimjlMmpb+4 NO+9I38uVaukDlOe4uothYY2RFLlgyf9RUYHUDBdK7kqyc/SqSEQQB4FEbyKgBcwfohxfbT42wv Tjyepc/O3rUuWkP9uIXXz1Qo1mtcMhKP2MfXI0y7SKCpRoYx+mBlcpf51TkvyGfH12xFU03Y1Xf +nDydiQy7WCdQKiyD16c4DiSfshVDfiVNA10FUcBFqK61qPOWXF7C+bXTF5TVX2vnbBn4jPwwaX BUnhGA0tPAKfUtaV5hg== 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=2026-01-09_04,2026-01-08_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 lowpriorityscore=0 bulkscore=0 malwarescore=0 priorityscore=1501 clxscore=1015 phishscore=0 spamscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2512120000 definitions=main-2601090110 Hi Peter. Thanks for going through. On 1/8/26 6:14 PM, Peter Zijlstra wrote: > On Wed, Jan 07, 2026 at 12:21:23PM +0530, Shrikanth Hegde wrote: >> NOHZ idle load balancer is kicked off only after time check. So move >> the atomic read after the time check to access it only when needed. >> >> When there are no idle CPUs(100% busy), even if the flag gets set to >> NOHZ_STATS_KICK | NOHZ_NEXT_KICK, find_new_ilb will fail and >> there will be no NOHZ idle balance. The current behaviour is retained. >> >> Note: This patch doesn't solve any cacheline overheads. No improvement >> in performance apart from saving a few cycles of atomic_read. > > Note that atomic_read() == READ_ONCE() is just a regular load, but sure. Cool. thanks. Let me keep it in the series then.