Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-07 Thread Steven Rostedt
On Fri, 2012-09-07 at 09:00 +0200, Peter Zijlstra wrote: > On Thu, 2012-09-06 at 15:22 -0700, Paul E. McKenney wrote: > > Ah! > > > > It is perfectly legal to avoid -starting- an RCU grace period for a > > minute, or even longer. If RCU has nothing to do, in other words, if no > > one registers a

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-07 Thread Peter Zijlstra
On Thu, 2012-09-06 at 15:22 -0700, Paul E. McKenney wrote: > Ah! > > It is perfectly legal to avoid -starting- an RCU grace period for a > minute, or even longer. If RCU has nothing to do, in other words, if no > one registers any RCU callbacks, then RCU need not start a grace period. > > Of cou

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-06 Thread Paul E. McKenney
On Thu, Sep 06, 2012 at 06:05:53PM -0400, Steven Rostedt wrote: > On Thu, 2012-09-06 at 14:58 -0700, Paul E. McKenney wrote: > > > > All these cases deserve a warning. > > > > Agreed, and that is the whole purpose of the stall warnings. > > Then let me ask the question again. According to the ch

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-06 Thread Steven Rostedt
On Thu, 2012-09-06 at 14:58 -0700, Paul E. McKenney wrote: > > All these cases deserve a warning. > > Agreed, and that is the whole purpose of the stall warnings. Then let me ask the question again. According to the change log: > If a given CPU avoids the idle loop but also avoids starting a ne

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-06 Thread Paul E. McKenney
On Thu, Sep 06, 2012 at 05:41:01PM -0400, Steven Rostedt wrote: > On Thu, 2012-09-06 at 14:03 -0700, Paul E. McKenney wrote: > > > Here are a few other ways that stalls can happen: > > > > o A CPU looping in an RCU read-side critical section. > > For a minute? That's a bug. > > > > > o

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-06 Thread Steven Rostedt
On Thu, 2012-09-06 at 14:03 -0700, Paul E. McKenney wrote: > Here are a few other ways that stalls can happen: > > o A CPU looping in an RCU read-side critical section. For a minute? That's a bug. > > o A CPU looping with interrupts disabled. This condition can > result in

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-06 Thread Paul E. McKenney
On Thu, Sep 06, 2012 at 05:19:18PM +0200, Peter Zijlstra wrote: > On Thu, 2012-09-06 at 11:07 -0400, Steven Rostedt wrote: > > On Thu, 2012-09-06 at 16:56 +0200, Peter Zijlstra wrote: > > > On Thu, 2012-08-30 at 11:56 -0700, Paul E. McKenney wrote: > > > > > > > > If a given CPU avoids the idle lo

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-06 Thread Peter Zijlstra
On Thu, 2012-09-06 at 11:07 -0400, Steven Rostedt wrote: > On Thu, 2012-09-06 at 16:56 +0200, Peter Zijlstra wrote: > > On Thu, 2012-08-30 at 11:56 -0700, Paul E. McKenney wrote: > > > > > > If a given CPU avoids the idle loop but also avoids starting a new > > > RCU grace period for a full minute

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-06 Thread Steven Rostedt
On Thu, 2012-09-06 at 16:56 +0200, Peter Zijlstra wrote: > On Thu, 2012-08-30 at 11:56 -0700, Paul E. McKenney wrote: > > > > If a given CPU avoids the idle loop but also avoids starting a new > > RCU grace period for a full minute, RCU can issue spurious RCU CPU > > stall warnings. This commit f

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-09-06 Thread Peter Zijlstra
On Thu, 2012-08-30 at 11:56 -0700, Paul E. McKenney wrote: > > If a given CPU avoids the idle loop but also avoids starting a new > RCU grace period for a full minute, RCU can issue spurious RCU CPU > stall warnings. This commit fixes this issue by adding a check for > ongoing grace period to avo

Re: [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-08-31 Thread Josh Triplett
On Thu, Aug 30, 2012 at 11:56:24AM -0700, Paul E. McKenney wrote: > From: "Paul E. McKenney" > > If a given CPU avoids the idle loop but also avoids starting a new > RCU grace period for a full minute, RCU can issue spurious RCU CPU > stall warnings. This commit fixes this issue by adding a chec

[PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU CPU stall warnings

2012-08-30 Thread Paul E. McKenney
From: "Paul E. McKenney" If a given CPU avoids the idle loop but also avoids starting a new RCU grace period for a full minute, RCU can issue spurious RCU CPU stall warnings. This commit fixes this issue by adding a check for ongoing grace period to avoid these spurious stall warnings. Reported