linux-kernel - Re: [PATCH tip/core/rcu 0/5] Fix for cond

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Message-ID: <20140620190434.GA22178@cloud>
Date:	Fri, 20 Jun 2014 12:04:34 -0700
From:	josh@...htriplett.org
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
	niv@...ibm.com, tglx@...utronix.de, peterz@...radead.org,
	rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com,
	dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com,
	sbw@....edu
Subject: Re: [PATCH tip/core/rcu 0/5] Fix for cond_resched performance
 regression

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@...htriplett.org>

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

- Josh Triplett
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