Re: tty^Wrcu/perf lockdep trace.

2013-10-07 Thread Paul E. McKenney
On Sat, Oct 05, 2013 at 09:28:02AM -0700, Paul E. McKenney wrote: > On Sat, Oct 05, 2013 at 06:05:11PM +0200, Peter Zijlstra wrote: > > On Fri, Oct 04, 2013 at 02:25:06PM -0700, Paul E. McKenney wrote: > > > > Why > > > > do we sti

Re: tty^Wrcu/perf lockdep trace.

2013-10-07 Thread Paul E. McKenney
On Mon, Oct 07, 2013 at 10:42:39AM +0200, Peter Zijlstra wrote: > On Sat, Oct 05, 2013 at 03:03:11PM -0700, Paul E. McKenney wrote: > > In theory, we could do that. But in practice, what would wake us up > > when the CPUs go non-idle? > > > > 1. We could do a wakeup on the idle-to-non-idle trans

Re: tty^Wrcu/perf lockdep trace.

2013-10-07 Thread Paul E. McKenney
On Mon, Oct 07, 2013 at 01:24:21PM +0200, Peter Zijlstra wrote: > On Fri, Oct 04, 2013 at 05:23:48PM -0700, Paul E. McKenney wrote: > > The underlying problem is that perf is invoking call_rcu() with the > > scheduler locks held, but in NOCB mode, call_rcu() will with high > > probability invoke th

Re: tty^Wrcu/perf lockdep trace.

2013-10-07 Thread Peter Zijlstra
On Fri, Oct 04, 2013 at 05:23:48PM -0700, Paul E. McKenney wrote: > The underlying problem is that perf is invoking call_rcu() with the > scheduler locks held, but in NOCB mode, call_rcu() will with high > probability invoke the scheduler -- which just might want to use its > locks. The reason tha

Re: tty^Wrcu/perf lockdep trace.

2013-10-07 Thread Peter Zijlstra
On Sat, Oct 05, 2013 at 03:03:11PM -0700, Paul E. McKenney wrote: > In theory, we could do that. But in practice, what would wake us up > when the CPUs go non-idle? > > 1.We could do a wakeup on the idle-to-non-idle transition. That > would increase idle-to-non-idle latency, defeating

Re: tty^Wrcu/perf lockdep trace.

2013-10-05 Thread Paul E. McKenney
On Sat, Oct 05, 2013 at 09:59:49PM +0200, Peter Zijlstra wrote: > On Sat, Oct 05, 2013 at 09:28:02AM -0700, Paul E. McKenney wrote: > > On Sat, Oct 05, 2013 at 06:05:11PM +0200, Peter Zijlstra wrote: > > > On Fri, Oct 04, 2013 at 02:25:06PM -0700, Paul E. McKenney wrote: > > > > >

Re: tty^Wrcu/perf lockdep trace.

2013-10-05 Thread Peter Zijlstra
On Sat, Oct 05, 2013 at 09:28:02AM -0700, Paul E. McKenney wrote: > On Sat, Oct 05, 2013 at 06:05:11PM +0200, Peter Zijlstra wrote: > > On Fri, Oct 04, 2013 at 02:25:06PM -0700, Paul E. McKenney wrote: > > > > Why > > > > do we sti

Re: tty^Wrcu/perf lockdep trace.

2013-10-05 Thread Paul E. McKenney
On Sat, Oct 05, 2013 at 06:05:11PM +0200, Peter Zijlstra wrote: > On Fri, Oct 04, 2013 at 02:25:06PM -0700, Paul E. McKenney wrote: > > > Why > > > do we still have a per-cpu kthread in nocb mode? The idea is that we do > > > not d

Re: tty^Wrcu/perf lockdep trace.

2013-10-05 Thread Peter Zijlstra
On Fri, Oct 04, 2013 at 02:25:06PM -0700, Paul E. McKenney wrote: > > Why > > do we still have a per-cpu kthread in nocb mode? The idea is that we do > > not disturb the cpu, right? So I suppose these kthreads get to run on > > ano

Re: tty^Wrcu/perf lockdep trace.

2013-10-04 Thread Paul E. McKenney
On Fri, Oct 04, 2013 at 03:02:32PM -0700, Paul E. McKenney wrote: > On Fri, Oct 04, 2013 at 02:25:06PM -0700, Paul E. McKenney wrote: > > On Fri, Oct 04, 2013 at 08:52:39PM +0200, Peter Zijlstra wrote: > > > On Fri, Oct 04, 2013 at 10:09:54AM -0700, Paul E. McKenney wrote: > > > > On Fri, Oct 04, 2

Re: tty^Wrcu/perf lockdep trace.

2013-10-04 Thread Paul E. McKenney
On Fri, Oct 04, 2013 at 02:25:06PM -0700, Paul E. McKenney wrote: > On Fri, Oct 04, 2013 at 08:52:39PM +0200, Peter Zijlstra wrote: > > On Fri, Oct 04, 2013 at 10:09:54AM -0700, Paul E. McKenney wrote: > > > On Fri, Oct 04, 2013 at 06:50:44PM +0200, Peter Zijlstra wrote: > > > > On Fri, Oct 04, 201

Re: tty^Wrcu/perf lockdep trace.

2013-10-04 Thread Paul E. McKenney
On Fri, Oct 04, 2013 at 08:52:39PM +0200, Peter Zijlstra wrote: > On Fri, Oct 04, 2013 at 10:09:54AM -0700, Paul E. McKenney wrote: > > On Fri, Oct 04, 2013 at 06:50:44PM +0200, Peter Zijlstra wrote: > > > On Fri, Oct 04, 2013 at 09:03:52AM -0700, Paul E. McKenney wrote: > > > > The problem exists,

Re: tty^Wrcu/perf lockdep trace.

2013-10-04 Thread Peter Zijlstra
On Fri, Oct 04, 2013 at 10:09:54AM -0700, Paul E. McKenney wrote: > On Fri, Oct 04, 2013 at 06:50:44PM +0200, Peter Zijlstra wrote: > > On Fri, Oct 04, 2013 at 09:03:52AM -0700, Paul E. McKenney wrote: > > > The problem exists, but NOCB made it much more probable. With non-NOCB > > > kernels, an i

Re: tty^Wrcu/perf lockdep trace.

2013-10-04 Thread Paul E. McKenney
On Fri, Oct 04, 2013 at 06:50:44PM +0200, Peter Zijlstra wrote: > On Fri, Oct 04, 2013 at 09:03:52AM -0700, Paul E. McKenney wrote: > > The problem exists, but NOCB made it much more probable. With non-NOCB > > kernels, an irq-disabled call_rcu() invocation does a wake_up() only if > > there are m

Re: tty^Wrcu/perf lockdep trace.

2013-10-04 Thread Peter Zijlstra
On Fri, Oct 04, 2013 at 09:03:52AM -0700, Paul E. McKenney wrote: > The problem exists, but NOCB made it much more probable. With non-NOCB > kernels, an irq-disabled call_rcu() invocation does a wake_up() only if > there are more than 10,000 callbacks stacked up on the CPU. With a NOCB > kernel,

Re: tty^Wrcu/perf lockdep trace.

2013-10-04 Thread Paul E. McKenney
On Fri, Oct 04, 2013 at 09:03:52AM -0700, Paul E. McKenney wrote: > On Fri, Oct 04, 2013 at 08:58:35AM +0200, Peter Zijlstra wrote: > > On Thu, Oct 03, 2013 at 12:58:32PM -0700, Paul E. McKenney wrote: > > > On Thu, Oct 03, 2013 at 09:42:26PM +0200, Peter Zijlstra wrote: > > > > > > > > That's not

Re: tty^Wrcu/perf lockdep trace.

2013-10-04 Thread Paul E. McKenney
On Fri, Oct 04, 2013 at 08:58:35AM +0200, Peter Zijlstra wrote: > On Thu, Oct 03, 2013 at 12:58:32PM -0700, Paul E. McKenney wrote: > > On Thu, Oct 03, 2013 at 09:42:26PM +0200, Peter Zijlstra wrote: > > > > > > That's not tty; that's RCU.. > > > > > > On Thu, Oct 03, 2013 at 03:08:30PM -0400, Da

Re: tty^Wrcu/perf lockdep trace.

2013-10-03 Thread Peter Zijlstra
On Thu, Oct 03, 2013 at 12:58:32PM -0700, Paul E. McKenney wrote: > On Thu, Oct 03, 2013 at 09:42:26PM +0200, Peter Zijlstra wrote: > > > > That's not tty; that's RCU.. > > > > On Thu, Oct 03, 2013 at 03:08:30PM -0400, Dave Jones wrote: > > > =

Re: tty^Wrcu/perf lockdep trace.

2013-10-03 Thread Paul E. McKenney
On Thu, Oct 03, 2013 at 09:42:26PM +0200, Peter Zijlstra wrote: > > That's not tty; that's RCU.. > > On Thu, Oct 03, 2013 at 03:08:30PM -0400, Dave Jones wrote: > > == > > [ INFO: possible circular locking dependency detected ] > > 3.12.0-rc3

Re: tty^Wrcu/perf lockdep trace.

2013-10-03 Thread Peter Zijlstra
That's not tty; that's RCU.. On Thu, Oct 03, 2013 at 03:08:30PM -0400, Dave Jones wrote: > == > [ INFO: possible circular locking dependency detected ] > 3.12.0-rc3+ #92 Not tainted > --- >