Re: [rcu_sched stall] regression/miss-config ?

[santosh.shilimkar@xxxxxxxxxx]

On 5/16/16 5:58 PM, Paul E. McKenney wrote:
> On Mon, May 16, 2016 at 12:49:41PM -0700, Santosh Shilimkar wrote:
> > On 5/16/2016 10:34 AM, Paul E. McKenney wrote:
> > > On Mon, May 16, 2016 at 09:33:57AM -0700, Santosh Shilimkar wrote:

[...]

> > > Are you running CONFIG_NO_HZ_FULL=y?  If so, the problem might be that
> > > you need more housekeeping CPUs than you currently have configured.
> > Yes, CONFIG_NO_HZ_FULL=y. Do you mean "CONFIG_NO_HZ_FULL_ALL=y" for
> > book keeping. Seems like without that clock-event code will just use
> > CPU0 for things like broadcasting which might become bottleneck.
> > This could explain connect the hrtimer_interrupt() path getting slowed
> > down because of book keeping bottleneck.
> >
> > $cat .config | grep NO_HZ
> > CONFIG_NO_HZ_COMMON=y
> > # CONFIG_NO_HZ_IDLE is not set
> > CONFIG_NO_HZ_FULL=y
> > # CONFIG_NO_HZ_FULL_ALL is not set
> > # CONFIG_NO_HZ_FULL_SYSIDLE is not set
> > CONFIG_NO_HZ=y
> > # CONFIG_RCU_FAST_NO_HZ is not set
>
> Yes, CONFIG_NO_HZ_FULL_ALL=y would give you only one CPU for all
> housekeeping tasks, including the RCU grace-period kthreads.  So you are
> booting without any nohz_full boot parameter?  You can end up with the
> same problem with CONFIG_NO_HZ_FULL=y and the nohz_full boot parameter
> that you can with CONFIG_NO_HZ_FULL_ALL=y.
I see. Yes, the systems are booting without nohz_full boot parameter.
Will try to add more CPUs to it & update the thread
after the verification since it takes time to reproduce the issue.

Thanks for discussion so far Paul. Its very insightful for me.

Regards,
Santosh