Re: [PATCH tip/core/rcu 0/5] Fix for cond_resched performance regression

[josh]

On Fri, Jun 20, 2014 at 11:32:49AM -0700, Paul E. McKenney wrote:
> Hello!
> 
> This series contains changes to address the performance regressions
> introduced by commit ac1bea85781e (Make cond_resched() report RCU
> quiescent states), which was in turn fixing a problem where tasks looping
> in the kernel could delay RCU grace periods.  The changes in this series
> are as follows:
> 
> 1.	Reduce the overhead of checking added to cond_resched() and friends.
> 
> 2.	Add a new cond_resched_rcu_qs() to provide RCU quiescent states
> 	even if cond_resched() should stop doing so.
> 
> 3.	Add a new RCU_COND_RESCHED_QS to prevent cond_resched() from
> 	reporting RCU quiescent states.
> 
> 4.	Prevent rcutorture testing from reporting spurious RCU CPU stall
> 	warnings, and also to test RCU_COND_RESCHED_QS.
> 
> 5.	Provides a boot/sysfs rcutree.jiffies_till_cond_resched_qs
> 	parameter to replace the magic "7".

For all five patches:

Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>

Glad to see this doesn't add any overhead to rcutiny.

- Josh Triplett
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