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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 Oct 2025 03:03:25.0667 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: b8b739a8-aab9-44ac-aa4f-08de15ce8fac 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=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN1PEPF00004681.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB8217 Hello Aaron, On 10/27/2025 5:32 PM, Aaron Lu wrote: > On Mon, Oct 27, 2025 at 05:05:34PM +0800, Hao Jia wrote: >> @@ -6403,7 +6407,7 @@ static void do_sched_cfs_slack_timer(struct cfs_bandwidth *cfs_b) >> * expired/exceeded, otherwise it may be allowed to steal additional ticks of >> * runtime as update_curr() throttling can not trigger until it's on-rq. >> */ >> -static void check_enqueue_throttle(struct cfs_rq *cfs_rq) >> +static void check_enqueue_throttle(struct cfs_rq *cfs_rq, int flags) >> { >> if (!cfs_bandwidth_used()) >> return; >> @@ -6418,6 +6422,13 @@ static void check_enqueue_throttle(struct cfs_rq *cfs_rq) >> >> /* update runtime allocation */ >> account_cfs_rq_runtime(cfs_rq, 0); >> + /* >> + * Do not attempt to throttle on the cfs_rq unthrottle path. >> + * and it must be placed after account_cfs_rq_runtime() to >> + * prevent a possible missed start of the bandwidth timer. > > Hi Prateek and Hao, > > Does it matter to start the bw timer? If no cfs_rq gets throttled, the > timer doesn't look that useful. Ack! But if we've reached here with ENQUEUE_THROTTLE set, we are in fact trying to enqueue a task during unthrottling and we only start the timer if we don't have any bandwidth since __account_cfs_rq_runtime() would bail out if "cfs_rq->runtime_remaining > 0" > Also, account_cfs_rq_runtime() calls > assign_cfs_rq_runtime() and if assign failed, it will do resched_curr() > but since we do not throttle cfs_rq here, that resched would be useless. resched only happens if "cfs_rq->curr" is set andcheck_enqueue_throttle() already bails out if "cfs_rq->curr" is set so the resched is avoided. -- Thanks and Regards, Prateek