Re: [External] Re: [PATCH v4 4/4] sched/core: Avoid multiple calling update_rq_clock() in unthrottle_offline_cfs_rqs()

[Hao Jia]

On 2023/6/9 Benjamin Segall wrote:
> Hao Jia <jiahao.os@xxxxxxxxxxxxx> writes:
>
> > This WARN_DOUBLE_CLOCK warning is triggered during cpu offline.
> > ------------[ cut here ]------------
> > rq->clock_update_flags & RQCF_UPDATED
> > WARNING: CPU: 0 PID: 3323 at kernel/sched/core.c:741
> > update_rq_clock+0xaf/0x180
> > Call Trace:
> >   <TASK>
> >   unthrottle_cfs_rq+0x4b/0x300
> >   rq_offline_fair+0x89/0x90
> >   set_rq_offline.part.118+0x28/0x60
> >   rq_attach_root+0xc4/0xd0
> >   cpu_attach_domain+0x3dc/0x7f0
> >   partition_sched_domains_locked+0x2a5/0x3c0
> >   rebuild_sched_domains_locked+0x477/0x830
> >   rebuild_sched_domains+0x1b/0x30
> >   cpuset_hotplug_workfn+0x2ca/0xc90
> >   ? balance_push+0x56/0xf0
> >   ? _raw_spin_unlock+0x15/0x30
> >   ? finish_task_switch+0x98/0x2f0
> >   ? __switch_to+0x291/0x410
> >   ? __schedule+0x65e/0x1310
> >   process_one_work+0x1bc/0x3d0
> >   worker_thread+0x4c/0x380
> >   ? preempt_count_add+0x92/0xa0
> >   ? rescuer_thread+0x310/0x310
> >   kthread+0xe6/0x110
> >   ? kthread_complete_and_exit+0x20/0x20
> >   ret_from_fork+0x1f/0x30
> >
> > The rq clock has been updated before the set_rq_offline()
> > function runs, so we don't need to call update_rq_clock() in
> > unthrottle_offline_cfs_rqs().
>
> I don't think we do in the path from rq_attach_root (though that's easy
> enough to fix, of course).

Thanks for your review.

Now our fix method is that after applying patch1, we update the rq clock 
before set_rq_offline(). Then use rq_clock_{start, stop}_loop_update to 
avoid updating the rq clock multiple times in unthrottle_cfs_rq().

Do you have any better suggestions?

Thanks,
Hao