Hi, On 09/26/2018 11:50 AM, Wanpeng Li wrote: > Hi Dietmar, > On Tue, 28 Aug 2018 at 22:55, Dietmar Eggemann <dietmar.eggem...@arm.com> > wrote: >> >> On 08/27/2018 12:14 PM, Peter Zijlstra wrote: >>> On Fri, Aug 24, 2018 at 02:24:48PM -0700, Steve Muckle wrote: >>>> On 08/24/2018 02:47 AM, Peter Zijlstra wrote: >>>>>>> On 08/17/2018 11:27 AM, Steve Muckle wrote:
[...] >>>>>>>> - later, when the prio is deboosted and the task is moved back >>>>>>>> to the fair class, the fair rq's min_vruntime is added to >>>>>>>> the task's vruntime, even though it wasn't subtracted earlier. > > Could you point out when the fair rq's min_vruntime is added to the > task's vruntime in your *later* scenario? attach_task_cfs_rq will not > do that the same reason as detach_task_cfs_rq. fair task's > sched_remote_wakeup is false which results in vruntime will not be > renormalized in enqueue_entity. The cfs_rq->min_vruntime is still added to the se->vruntime in enqueue_task_fair(). It's just that without this patch, which adds the '&& p->sched_remote_wakeup' bit to the condition under which vruntime_normalized() returns true, detach_task_cfs_rq() won't go into the 'if (!vruntime_normalized(p))' path and not subtract cfs_rq->min_vruntime from se->vruntime. Since 'task_cpu(p) equal cpu' in try_to_wake_up() for the fair task, WF_MIGRATED is not set and set_task_cpu() -> migrate_task_rq_fair() is not called which could subtract cfs_rq->min_vruntime from se->vruntime as well. My former example with a different set of trace events: fair_task-3580 [004] 35.389346: sched_stat_runtime: comm=fair_task pid=3580 runtime=45312 [ns] vruntime=46922871 [ns] <-- se->vruntime=46.922.871 ... rt_task-3579 [000] 35.391573: sched_waking: comm=fair_task pid=3580 prio=120 target_cpu=004 ... rt_task-3579 [000] 35.391627: sched_pi_setprio: comm=fair_task pid=3580 oldprio=120 newprio=19 ... rt_task-3579 [000] 35.391661: bprint: detach_task_cfs_rq: task=fair_task pid=3580 cpu=4 vruntime_normalized=1 rt_task-3579 [000] 35.391706: sched_switch: rt_task:3579 [19] D ==> swapper/0:0 [120] <idle>-0 [004] 35.391834: sched_wakeup: fair_task:3580 [19] success=1 CPU:004 <idle>-0 [004] 35.391840: sched_switch: swapper/4:0 [120] S ==> fair_task:3580 [19] fair_task-3580 [004] 35.391853: sched_pi_setprio: comm=fair_task pid=3580 oldprio=19 newprio=120 ... fair_task-3580 [004] 35.391863: bprint: enqueue_task_fair: task=fair_task pid=3580 curr=0 se->vruntime=93845742 cpu=4 cfs_rq->min_vruntime=46922871 ... fair_task-3580 [004] 35.391877: sched_waking: comm=rt_task pid=3579 prio=19 target_cpu=000 ... fair_task-3580 [004] 35.391885: sched_stat_runtime: comm=fair_task pid=3580 runtime=31250 [ns] vruntime=93876992 [ns] <-- se->vruntime=93.876.992
