linux-kernel - Re: [PATCH tip/core/rcu 02/11] rcu: Expedite during suspend and resume only on smallish systems

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Message-ID: <20130818031831.GM28923@leaf>
Date:	Sat, 17 Aug 2013 20:18:32 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com,
	edumazet@...gle.com, darren@...art.com, fweisbec@...il.com,
	sbw@....edu
Subject: Re: [PATCH tip/core/rcu 02/11] rcu: Expedite during suspend and
 resume only on smallish systems

On Sat, Aug 17, 2013 at 06:37:47PM -0700, Paul E. McKenney wrote:
> From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
> 
> Expedited grace periods are of dubious benefit on very large systems,
> so this commit restricts their automated use during suspend and resume
> to systems of 256 or fewer CPUs.
> 
> Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>

This seems odd.  If expedited grace periods don't help on large systems,
shouldn't you just compile them out entirely and ignore rcu_expedited,
rather than just in this one special case?

In any case, if this patch still makes sense, please squash it into the
previous one.

- Josh Triplett
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