linux-kernel - Re: [PATCH 3/3] hotplug: Optimize cpu_hotplug_{begin,done}() using rcu

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Message-ID: <20131003184607.GQ5790@linux.vnet.ibm.com>
Date:	Thu, 3 Oct 2013 11:46:07 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Oleg Nesterov <oleg@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] hotplug: Optimize cpu_hotplug_{begin,done}() using
 rcu_sync

On Thu, Oct 03, 2013 at 08:41:51PM +0200, Peter Zijlstra wrote:
> On Thu, Oct 03, 2013 at 09:48:38AM -0700, Paul E. McKenney wrote:
> > > -enum { readers_fast = 0, readers_slow, readers_block };
> > > +enum { readers_slow, readers_block };
> > 
> > It took me a bit to realize that readers_fast is obsoleted by the
> > rcu_sync_is_idle() above.  ;-)
> 
> Yeah.. I pondered changing/adding to the rcu_sync interface to allow
> using gp_count like status to avoid the extra variable, but decided
> against it for now.

Should be OK as is -- people who haven't reviewed the old version with
readers_fast are unlikely to be confused by the current setup.

							Thanx, Paul

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