On Sun, Aug 20, 2017 at 11:35:14AM -0700, Paul E. McKenney wrote:
> On Sun, Aug 20, 2017 at 11:00:40PM +1000, Nicholas Piggin wrote:
> > On Sun, 20 Aug 2017 14:45:53 +1000
> > Nicholas Piggin <npig...@gmail.com> wrote:
> >
> > > On Wed, 16 Aug 2017 09:27:31 -0700
> > > "Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote:
> > > > On Wed, Aug 16, 2017 at 05:56:17AM -0700, Paul E. McKenney wrote:
> > > >
> > > > Thomas, John, am I misinterpreting the timer trace event messages?
> > >
> > > So I did some digging, and what you find is that rcu_sched seems to do a
> > > simple scheudle_timeout(1) and just goes out to lunch for many seconds.
> > > The process_timeout timer never fires (when it finally does wake after
> > > one of these events, it usually removes the timer with del_timer_sync).
> > >
> > > So this patch seems to fix it. Testing, comments welcome.
> >
> > Okay this had a problem of trying to forward the timer from a timer
> > callback function.
> >
> > This was my other approach which also fixes the RCU warnings, but it's
> > a little more complex. I reworked it a bit so the mod_timer fast path
> > hopefully doesn't have much more overhead (actually by reading jiffies
> > only when needed, it probably saves a load).
>
> Giving this one a whirl!
No joy here, but then again there are other reasons to believe that I
am seeing a different bug than Dave and Jonathan are.
OK, not -entirely- without joy -- 10 of 14 runs were error-free, which
is a good improvement over 0 of 84 for your earlier patch. ;-) But
not statistically different from what I see without either patch.
But no statistical difference compared to without patch, and I still
see the "rcu_sched kthread starved" messages. For whatever it is worth,
by the way, I also see this: "hrtimer: interrupt took 5712368 ns".
Hmmm... I am also seeing that without any of your patches. Might
be hypervisor preemption, I guess.
Thanx, Paul
PS. I will be off the grid for the next day or so. Eclipse day here...
