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

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Message-ID: <20090622170831.GF6754@linux.vnet.ibm.com>
Date:	Mon, 22 Jun 2009 10:08:31 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Darren Hart <dvhltc@...ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	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 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.  ;-)

						Thanx, Paul
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