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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?r+YPZ9NqEvfH+czQt8yKS57xCpMkEA7PNnLQ6JA1tyJmrnAZG/yDuzx37r8y?= =?us-ascii?Q?2nmUhqGB2MzEZ6kM3/tAgVGUUprfxF83mFY0SGdZUnECQQFOKtgi1kHpiWL/?= =?us-ascii?Q?Qp/xAYFNMNAxrqnM9GGS3hyhrrBjUt1Nb/tppivxp7xHsP7dk4/ZuZZ/nfcj?= =?us-ascii?Q?xMlCe6P4QgmyVTml9fT1aDq9kSRQyQjeuieZoadUbIU1RmmTrCOOEP+PMlHr?= =?us-ascii?Q?EhS/QzJbZKboxiTLG2DSyYIe7G6vpt7GAtxu4T9cM5QpWah16zA82gsAfXk4?= =?us-ascii?Q?lQSi2UKo1l85a4Xzj4FDwo5YJ24TkG032XTBgHnPTZ4CqoF1vILBLzzDFawx?= =?us-ascii?Q?bvhzEkMLmEisbSHYas2BM0AW4/e+ZPjCDWX+0pO93o0YKUHxp8g8SCEkiS1Q?= =?us-ascii?Q?yHevmgdgZ8b+rVJZ8oG+uKSwN/ZYcbQVYgTw6mpwH3yOYfj1MiNv9DOBICK8?= =?us-ascii?Q?EpEwvVlN4twaZGHaaSEL5ztzpCwHUCR6Y7amRBmG1TfPVrc0pEz+vvXnCfUZ?= =?us-ascii?Q?E52zbG6zlCSoz7GlV+jMXOsANBrio48yuhfapl5kh5yQ+/5ttYXZuCafcgLF?= =?us-ascii?Q?Gyz5OsgAfjhu9DppAwes730vLx6juwOofOAF+WZ6CkE4o7iRwVDI1mSBpMbJ?= =?us-ascii?Q?j+CZkw8FcL07f7EhCkWNhaVO0yrJBIrOAcRPued8BHqohK5dsjjt5AjXW0RP?= =?us-ascii?Q?btwuZ0Q5pQJ8jfiS5cKqwMSvYgKZEjjWTUTvXhF4+IwObRa9iTSNPs4zuO2C?= =?us-ascii?Q?IPW/GdQQmuYg8WoY8sJPSdjBaUuN/Svk6a8TEwAfBOuH8DKHz6x4f/pvq7TU?= =?us-ascii?Q?siTnntDzbDoJ4YsrO2quBZF5+S6JOwymjp+GOILKiLdYC0NOJp4uRtNMXvdK?= =?us-ascii?Q?NmnJWissHnu6Gestpm+po2DNCzXXb1Eu5GPnyyMZNs0yDUOc0ZPAq3tq4Zh+?= =?us-ascii?Q?tFX3JQvFQ1QAXAxFunUTY7l6hKvF4c2DD/w3KbUOx03nuBq0SCljplHQdYGO?= =?us-ascii?Q?ff9foTLMGdAVDFszis9JpcGBSw+Oda0PqNtFvQXASp/dMjljprWGQ6mdvxVO?= =?us-ascii?Q?0bF248BBGJJ7Y6x16zTkso6SKsy5kJsdTJ8xqvaW30xIGw7BvORzYgpMWSdG?= =?us-ascii?Q?CovJsnfmz8ZacQwe+meAk/CznpzV3EIiWIsJI4+fwBu2sGpd8oxVytdRnnVp?= =?us-ascii?Q?eSxvnbF9gnNgUbqNYgJe+j1hVmY3u+hNYJv2790/35pZ2y8tCWwITORmcC6K?= =?us-ascii?Q?41BdrDlegek4FnKvOO9kMQsGg1odnM9Ypmq2dUNLWxzKRzNxcR4k67GMNlF+?= =?us-ascii?Q?Q3JpPViYWpYt+Yqn8v1edgwJ0IG5rjfPUpMV4p5/6E8+xwdYbk4T2KhQ43nT?= =?us-ascii?Q?SQ5HLcI93k5y5FiM4aA0wNPH9y3mQcL0pOiMzFc1h3KFeKO/eeGmcZAlMO+U?= =?us-ascii?Q?P6iBXOxywiMWIpSl2qaBQ1n9fhFW8fAfzEbPZVGeinyF9c4SkG2mXJJcthQv?= =?us-ascii?Q?gSlmk4VWeho/7q0nGlmXq+oO18jeFbsCMuCGS+7ShL8pu/zMjMGb4DvKOW26?= =?us-ascii?Q?IdQ9mFm6si6bozFIpM8X7kl7ZPq8iTLB17aEblv5?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: e111b8a1-8fed-401f-dc95-08de1c71ea36 X-MS-Exchange-CrossTenant-AuthSource: LV8PR12MB9620.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Nov 2025 13:47:52.2076 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: pxkC3uM54cs89rUyAaP1ApyCiXG86fagMbmGPceJu1fAcE2sbehvmEp+AiGPametTB6bHlpVLD0BBie31h2EkA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR12MB999089 On Wed, Oct 29, 2025 at 08:08:37PM +0100, Andrea Righi wrote: > sched_ext tasks can be starved by long-running RT tasks, especially since > RT throttling was replaced by deadline servers to boost only SCHED_NORMAL > tasks. > > Several users in the community have reported issues with RT stalling > sched_ext tasks. This is fairly common on distributions or environments > where applications like video compositors, audio services, etc. run as RT > tasks by default. > > Example trace (showing a per-CPU kthread stalled due to the sway Wayland > compositor running as an RT task): > > runnable task stall (kworker/0:0[106377] failed to run for 5.043s) > ... > CPU 0 : nr_run=3 flags=0xd cpu_rel=0 ops_qseq=20646200 pnt_seq=45388738 > curr=sway[994] class=rt_sched_class > R kworker/0:0[106377] -5043ms > scx_state/flags=3/0x1 dsq_flags=0x0 ops_state/qseq=0/0 > sticky/holding_cpu=-1/-1 dsq_id=0x8000000000000002 dsq_vtime=0 slice=20000000 > cpus=01 > > This is often perceived as a bug in the BPF schedulers, but in reality > schedulers can't do much: RT tasks run outside their control and can > potentially consume 100% of the CPU bandwidth. > > Fix this by adding a sched_ext deadline server, so that sched_ext tasks are > also boosted and do not suffer starvation. > > Two kselftests are also provided to verify the starvation fixes and > bandwidth allocation is correct. Peter, Juri, this has now been tested quite extensively on our side and we're considering applying these patches to Tejun's sched_ext branch. Do you have any objections or concerns? Thanks, -Andrea