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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 14 Jan 2026 06:47:18.8510 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: e6b3564e-8f31-4375-9029-08de5338c312 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SA2PEPF00001507.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW3PR12MB4395 Hello Peter, On 1/13/2026 5:17 PM, Peter Zijlstra wrote: > Hum... so this one is a little more tricky. > > So the normal rules are that DEQUEUE_SAVE + ENQUEUE_RESTORE should be as > invariant as possible. > > But what I think happens here is that at the point of dequeue we are > effectively ready to throttle/replenish, but we don't. > > Then at enqueue, we do. The replenish changes the deadline and we're up > a creek. I've the following data from the scenario in which I observe the same splat as Pierre splat wit the two fixes on top of tip: yes-4108 [194] d..2. 53.396872: get_prio_dl: get_prio_dl: clock(53060728757) yes-4108 [194] d..2. 53.396873: update_curr_dl_se: update_curr_dl_se: past throttle label yes-4108 [194] d..2. 53.396873: update_curr_dl_se: dl_throttled(0) dl_overrun(0) timer_queued(0) server?(0) yes-4108 [194] d..2. 53.396873: update_curr_dl_se: dl_se->runtime(190623) rq->dl.overloaded(0) yes-4108 [194] d..2. 53.396874: get_prio_dl: get_prio_dl: deadline(53060017809) yes-4108 [194] d..2. 53.396878: enqueue_dl_entity: ENQUEUE_RESTORE update_dl_entity yes-4108 [194] d..2. 53.396878: enqueue_dl_entity: setup_new_dl_entity yes-4108 [194] d..2. 53.396878: enqueue_dl_entity: Replenish: Old: 53060017809 dl_deadline(1000000) yes-4108 [194] d..2. 53.396879: enqueue_dl_entity: Replenish: New: 53061728757 yes-4108 [194] d..2. 53.396882: prio_changed_dl.part.0: Woops! prio_changed_dl: CPU(194) clock(53060728757) overloaded(0): Task: yes(4108), Curr: yes(4108) deadline: 53060017809 -> 53061728757 get_prio_dl() sees "deadline < rq->clock" but dl_se->runtime is still positive so update_curr_dl_se() doesn't fiddle with the deadline. ENQUEUE_RESTORE sees "deadline" before "rq->clock" and calls setup_new_dl_entity() which calls replenish. sched_change_end() will call prio_changed() with the old deadline from get_prio_dl() but enqueue advanced the deadline so we land in a pickle. > > Let me think about this for a bit... Should prio_changed_dl() care about "dl_se->dl_deadline" having changed within the sched_change guard since that is the attribute that can be changed using sched_setattr() right? -- Thanks and Regards, Prateek