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

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Date:	Tue, 23 Jun 2009 11:48:46 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
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


* 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 ;-)

	Ingo
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