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Tue, 11 Nov 2025 06:24:06 +0000 (GMT) Message-ID: Date: Tue, 11 Nov 2025 11:54:05 +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 v4] sched/fair: Skip sched_balance_running cmpxchg when balance is not due To: Tim Chen Cc: Ingo Molnar , Chen Yu , Doug Nelson , Mohini Narkhede , linux-kernel@vger.kernel.org, Vincent Guittot , K Prateek Nayak , Peter Zijlstra References: <6fed119b723c71552943bfe5798c93851b30a361.1762800251.git.tim.c.chen@linux.intel.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <6fed119b723c71552943bfe5798c93851b30a361.1762800251.git.tim.c.chen@linux.intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: A8zxKZIyHUsG9f-1IcC-3DSNlzWwmrZY X-Proofpoint-ORIG-GUID: A8zxKZIyHUsG9f-1IcC-3DSNlzWwmrZY X-Authority-Analysis: v=2.4 cv=VMPQXtPX c=1 sm=1 tr=0 ts=6912d68b cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=QSENffHbnlRO23lpVA8A:9 a=QEXdDO2ut3YA:10 a=cPQSjfK2_nFv0Q5t_7PE:22 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTA4MDAyMiBTYWx0ZWRfX3t1kx9aUBm90 P2WhAUReCfeLZObBpx1U/8iXcVHR4P3KRzxl4PvzhHrQZ0r9FERyU4oxQ8SE6lLPR/1gIjgxxzx 3S9JyBi3tgUfP8SvfeNrngFOO7f3dQwNDWUpXRD7fWTXUprv6p8OXsiPFNEJUkhNxUSDHXBTObS tLPHRe6SID3HaWdhEvSKtaJIJdFmQzNEmNgB8JHR4wCOEd7+Rw5Bryk26hK2W2TVbSaT49aC/nv U6qY9lU3PkMlaSD3k9S3O70a1rCwjKY2ShPbIEn1mQ6xnQqtxE1P0A7wdx6T++bhBJja7uGGHuA LIhIgZ7jrRgYl6+nERbPd8tD6tr6SFfTgCzVDEludJwWAmhuwWFxQuz+tv4PJIM8madlH0FDzCB 42vnDTbqSXpq8NTYO7xTlBlWtzOpbQ== 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=2025-11-11_01,2025-11-10_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 priorityscore=1501 lowpriorityscore=0 bulkscore=0 clxscore=1015 phishscore=0 spamscore=0 malwarescore=0 adultscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511080022 Hi Tim, On 11/11/25 12:17 AM, Tim Chen wrote: > The NUMA sched domain sets the SD_SERIALIZE flag by default, allowing > only one NUMA load balancing operation to run system-wide at a time. > > Currently, each sched group leader directly under NUMA domain attempts > to acquire the global sched_balance_running flag via cmpxchg() before > checking whether load balancing is due or whether it is the designated > load balancer for that NUMA domain. On systems with a large number > of cores, this causes significant cache contention on the shared > sched_balance_running flag. > > This patch reduces unnecessary cmpxchg() operations by first checking > that the balancer is the designated leader for a NUMA domain from > should_we_balance(), and the balance interval has expired before > trying to acquire sched_balance_running to load balance a NUMA > domain. > > On a 2-socket Granite Rapids system with sub-NUMA clustering enabled, > running an OLTP workload, 7.8% of total CPU cycles were previously spent > in sched_balance_domain() contending on sched_balance_running before > this change. Looks good to me. Thanks for getting this into current shape. I see hackbench improving slightly across its variations. So, Tested-by: Shrikanth Hegde