linux-kernel - Re: [PATCH] v4 RCU: the bloatwatch edition

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Message-ID: <20090623125920.GB6872@linux.vnet.ibm.com>
Date:	Tue, 23 Jun 2009 05:59:20 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Darren Hart <dvhltc@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	linux-kernel@...r.kernel.org, niv@...ibm.com, lethal@...ux-sh.org,
	kernel@...tstofly.org, matthew@....cx
Subject: Re: [PATCH] v4 RCU: the bloatwatch edition

On Tue, Jun 23, 2009 at 11:48:46AM +0200, Ingo Molnar wrote:
> 
> * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > On Mon, Jun 22, 2009 at 09:30:29AM -0700, Darren Hart wrote:
> > > Paul E. McKenney wrote:
> > >> On Mon, Jun 22, 2009 at 08:29:41AM -0700, Andrew Morton wrote:
> > >>> On Mon, 22 Jun 2009 14:49:51 +0200 Ingo Molnar <mingo@...e.hu> wrote:
> > >>>
> > >>>> * David Howells <dhowells@...hat.com> wrote:
> > >>>>
> > >>>>> Hi Paul,
> > >>>>>
> > >>>>> Are you going to push your RCU patch for this merge window?
> > >>>> Andrew needs to be convinced for that to happen.
> > >>>>
> > >>> whome?  I rarely have firm opinions on anything.  iirc the question
> > >>> here was "is it worth adding another RCU implementation to save 900
> > >>> bytes"?
> > >>>
> > >>> I find it pretty hard to see how to come up with "yes" for that one but
> > >>> it's hardly a huge issue.  If you guys feel otherwise then go wild.
> > >> Well, I do need to pull the "expedited" interface into the bloatwatch
> > >> version, and my update of rcutorture made me realize that I can cut
> > >> out a few more bytes, so I will submit an update.  For what it is worth,
> > >> here are the opinions expressed on LKML:
> > >> +	Ingo Molnar: good documentation, minimal RCU implementation.
> > >> ?	Andi Kleen: will there be !SMP systems in the future?
> > >> +	Lennert Buytenhek: there will be !SMP ARM for a long time.
> > >> +	Paul Mundt: good idea for more-constrained SH platforms.
> > >> +	David Howells: Acked-by.  works on FRV board.
> > >> ?	Andrew Morton: do we really need another RCU implementation?
> > >> Of course, I well remember programming systems with 4K of core memory
> > >> back in the 1970s, and therefore feel a bit guilty about sticking deep
> > >> embedded platforms with the increase in memory footprint represented
> > >> by Hierarchical RCU compared to Classic RCU.  And Bloatwatch RCU is much
> > >> smaller and easier to understand/maintain than is Classic RCU.
> > >> So, again, I will forward port, optimize, test, and resubmit.
> > >
> > > IIRC, in previous threads on this topic, the Bloatwatch edition was 
> > > expected to replace Classic RCU.  If so, wouldn't that address Andrew's 
> > > concern of "adding" another implementation?
> > 
> > Andrew expressed a preference for dropping Classic RCU without 
> > adding Bloatwatch RCU.  ;-)
> 
> Yes. In Linux there's no forced 'tie-in' of features and we'll 
> brutally untie them and use the most productive combination, if 
> justified technically ;-)

;-)

							Thanx, Paul
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