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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Aug 2024 05:26:46.8412 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: ca885eca-679e-4cd5-1b3d-08dcb5d85db3 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=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SA2PEPF00001505.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: CY8PR12MB7633 Hello Tejun, Thank you for updating the commit message. On 8/6/2024 4:09 AM, Tejun Heo wrote: > balance_fair() skips newidle balancing if rq->nr_running - there are already > tasks on the rq, so no need to try to pull tasks. This tests the total > number of queued tasks on the CPU instead of only the fair class, but is > still correct as the rq can currently only have fair class tasks while > balance_fair() is running. > > However, with the addition of sched_ext below the fair class, this will not > hold anymore and make put_prev_task_balance() skip sched_ext's balance() > incorrectly as, when a CPU has only lower priority class tasks, > rq->nr_running would still be positive and balance_fair() would return 1 > even when fair doesn't have any tasks to run. > > Update balance_fair() to use sched_fair_runnable() which tests > rq->cfs.nr_running which is updated by bandwidth throttling. Note that > pick_next_task_fair() already uses sched_fair_runnable() in its optimized > path for the same purpose. > > v2: K Prateek Nayak pointed out that the bw control issue described in v1 > was incorrect. Patch description updated. As this makes the patch only > relevant for sched_ext, I'll carry this through the sched_ext tree > unless there are objections. > > Signed-off-by: Tejun Heo > Reported-by: Peter Zijlstra > Cc: K Prateek Nayak Looks good to me! Reviewed-by: K Prateek Nayak -- Thanks and Regards, Prateek > --- > kernel/sched/fair.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8323,7 +8323,7 @@ static void set_cpus_allowed_fair(struct > static int > balance_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) > { > - if (rq->nr_running) > + if (sched_fair_runnable(rq)) > return 1; > > return sched_balance_newidle(rq, rf) != 0;