linux-kernel - Re: [PATCH v2 1/2] workqueue: add quiescent state between work items

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Date:	Tue, 7 Oct 2014 20:24:11 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Joe Lawrence <joe.lawrence@...atus.com>
Cc:	Jiri Pirko <jiri@...nulli.us>, Tejun Heo <tj@...nel.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 1/2] workqueue: add quiescent state between work items

On Tue, Oct 07, 2014 at 01:45:28PM -0400, Joe Lawrence wrote:
> On Tue, 7 Oct 2014 06:43:29 -0700
> "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > On Tue, Oct 07, 2014 at 09:29:42AM +0200, Jiri Pirko wrote:
> [ ... snip ... ]
> > > 
> > > Paul, Tehun, how do you propose to fix this on older kernels which do
> > > not have rcu_note_voluntary_context_switch? I'm particullary interested
> > > in 3.10.
> > 
> > Hello, Jiri,
> > 
> > Older kernels can instead use rcu_note_context_switch().
> 
> Hi Paul,
> 
> Does 4a81e8328d37 ("rcu: Reduce overhead of cond_resched() checks for
> RCU") affect a backport to 3.10?
> 
> I noticed that rcu_note_context_switch added a call to
> rcu_momentary_dyntick_idle in that change, which is only present in
> v3.16+.
> 
> Would rcu_note_context_switch be effective by itself on a 3.10 kernel?

Should be fine.  There is more overhead than current mainline, but that
should not be in the noise compared to executing a work-queue item.

							Thanx, Paul

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