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Thu, 22 Jan 2026 03:53:10 +0000 (GMT) Message-ID: Date: Thu, 22 Jan 2026 09:23:09 +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] sched/fair: Disable scheduler feature NEXT_BUDDY To: Mel Gorman Cc: Peter Zijlstra , Ingo Molnar , Juri Lelli , Dietmar Eggemann , Valentin Schneider , Chris Mason , Ryan Roberts , linux-kernel@vger.kernel.org, Madadi Vineeth Reddy References: Content-Language: en-US From: Madadi Vineeth Reddy In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: CaPpK5_dofIAxu0pahb_afeezrcoP3it X-Proofpoint-ORIG-GUID: CaPpK5_dofIAxu0pahb_afeezrcoP3it X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMTIyMDAyNiBTYWx0ZWRfX38l/E31ZHE5P fErp6ZO4krI48n9T/GazPV0v5kRFNQHuJumB7fY2cWWe+A0FgxkkujoDfdQ586mL/W9fKqDK9PL BKlOojrf3H0niU7kYoeeefpji/mG6c4qAHienAAu1ae/wdj2Mv9FmBzZ1jyC4rdslcRDaCjpI7T kWmjfrEzoghVGjmaSb1QxVhCXymC3wkbQ2c2+1MFXzUVctOa3uawZLPCJ8lxYJTvHOtn+OTnyBv x0FN8cZkmIG5Ve6rY32VGxHJc9IDE/VxS0/kiR8AEo7zef6lENnhoG03kA3VvJS2FbXTVvPtAzH iwDHgaoXiu2ylLgtUFSg1I91lMdXcuQObPbCT5iyFQW9VHjn0irpL4c14lFwVzv97oBoJipffcT h5jaIACdd4fDxHlqBOGJ58lWlfMgz7opUIuiX47/14099+m71omWh8lS1YspqUV2WrjCk5I4UYQ eSAYNsmkRTIAd8H1uUg== X-Authority-Analysis: v=2.4 cv=bopBxUai c=1 sm=1 tr=0 ts=69719f2c cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=vUbySO9Y5rIA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=7CQSdrXTAAAA:8 a=VnNF1IyMAAAA:8 a=R_Myd5XaAAAA:8 a=YZrqWeNhcWuK_13INasA:9 a=QEXdDO2ut3YA:10 a=a-qgeE7W1pNrGK8U0ZQC:22 a=L2g4Dz8VuBQ37YGmWQah:22 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.20,FMLib:17.12.100.49 definitions=2026-01-21_04,2026-01-20_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 adultscore=0 suspectscore=0 impostorscore=0 phishscore=0 malwarescore=0 lowpriorityscore=0 priorityscore=1501 clxscore=1011 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2601150000 definitions=main-2601220026 On 20/01/26 17:03, Mel Gorman wrote: > NEXT_BUDDY was disabled with the introduction of EEVDF and enabled again > after NEXT_BUDDY was rewritten for EEVDF by commit e837456fdca8 ("sched/fair: > Reimplement NEXT_BUDDY to align with EEVDF goals"). It was not expected > that this would be a universal win without a crystal ball instruction > but the reported regressions are a concern [1][2] even if gains were > also reported. Specifically; > > o mysql with client/server running on different servers regresses > o specjbb reports lower peak metrics > o daytrader regresses > > The mysql is realistic and a concern. It needs to be confirmed if > specjbb is simply shifting the point where peak performance is measured > but still a concern. daytrader is considered to be representative of a > real workload. > > Access to test machines is currently problematic for verifying any fix to > this problem. Disable NEXT_BUDDY for now by default until the root causes > are addressed. > > Link: https://lore.kernel.org/lkml/4b96909a-f1ac-49eb-b814-97b8adda6229@arm.com [1] > Link: https://lore.kernel.org/lkml/ec3ea66f-3a0d-4b5a-ab36-ce778f159b5b@linux.ibm.com [2] > Signed-off-by: Mel Gorman > --- > kernel/sched/features.h | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sched/features.h b/kernel/sched/features.h > index 980d92bab8ab..136a6584be79 100644 > --- a/kernel/sched/features.h > +++ b/kernel/sched/features.h > @@ -29,7 +29,7 @@ SCHED_FEAT(PREEMPT_SHORT, true) > * wakeup-preemption), since its likely going to consume data we > * touched, increases cache locality. > */ > -SCHED_FEAT(NEXT_BUDDY, true) > +SCHED_FEAT(NEXT_BUDDY, false) Thanks Mel, this should fix the issue for now. I spent some time in limiting the number of times NEXT_BUDDY is selected consecutively which improved the Daytrader performance by around 2%. (out of the 7% regression). Will continue exploring it. Tested-by: Madadi Vineeth Reddy Thanks, Vineeth > > /* > * Allow completely ignoring cfs_rq->next; which can be set from various