> > > before starting throwing some patch into the the air I would like to align with you the approach we should take here. > > > > > > my suggestion here : > > >- ftrace infra should verify no migration happen (end and start happens on same CPU) in case not we will throw warning for the issue . > > > >The scheduler should have. On entering the ring buffer code > >ring_buffer_lock_reserver() it disables preemption and does not > >re-enable it until ring_buffer_unlock_commit(). > > > >The only way to migrate is if you re-enable preemption. WHICH IS A > >BUG! >So what on earth did that? >I'm guessing some driver's query_pkey op, but AFAIK we don't have any >explicit pre-emption reenablements in the code - unless it is sneaky.. trace infra uses preempt_disable_notrace/preempt_enable_notrace to disable/enable preemtion but my kernel compiled without CONFIG_PREEMPTION so this functions are only barriers - looks like the idea behind was to avoid involuntary preemtion but in our case it is a voluntary (there is a wait_for_completion in the query_pkey rabbit hole). so no scheduler here to warn about illegal migration. >Leonid what driver are you testing? mlx5 - (MLNX_OFED-5.3-1.0.0.1)
