On Sun, 20 Aug 2017 14:14:29 -0700 "Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote:
> 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. Okay it makes the warnings go away for me, but I'm just booting then leaving the system idle. You're doing some CPU hotplug activity? Thanks, Nick
