linux-kernel - Re: [PATCH tip/core/rcu] Reduce overhead of cond

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Message-ID: <20140623152656.GA22225@linux.vnet.ibm.com>
Date:	Mon, 23 Jun 2014 08:26:56 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Christoph Lameter <cl@...two.org>
Cc:	Josh Triplett <josh@...htriplett.org>,
	linux-kernel@...r.kernel.org, mingo@...nel.org,
	laijs@...fujitsu.com, dipankar@...ibm.com,
	akpm@...ux-foundation.org, mathieu.desnoyers@...icios.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, dave.hansen@...el.com,
	ak@...ux.intel.com, umgwanakikbuti@...il.com
Subject: Re: [PATCH tip/core/rcu] Reduce overhead of cond_resched() checks
 for RCU

On Mon, Jun 23, 2014 at 08:53:12AM -0500, Christoph Lameter wrote:
> On Fri, 20 Jun 2014, Paul E. McKenney wrote:
> 
> > > I like this approach *far* better.  This is the kind of thing I had in
> > > mind when I suggested using the fqs machinery: remove the poll entirely
> > > and just thwack a CPU if it takes too long without a quiescent state.
> > > Reviewed-by: Josh Triplett <josh@...htriplett.org>
> >
> > Glad you like it.  Not a fan of the IPI myself, but then again if you
> > are spending that must time looping in the kernel, an extra IPI is the
> > least of your problems.
> 
> Good. The IPI is only used when actually necessary. The code inserted
> was always there and always executed although rarely needed.

Interesting.  I actually proposed this approach several times in the
earlier thread, but to deafing silence: https://lkml.org/lkml/2014/6/18/836,
https://lkml.org/lkml/2014/6/17/793, and https://lkml.org/lkml/2014/6/20/479.

I guess this further validates interpreting silence as assent.

							Thanx, Paul

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