linux-kernel - Re: [PATCH, RFC, tip/core/rcu] scalable classic RCU implementation

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Message-ID: <20080827182801.GK6711@linux.vnet.ibm.com>
Date:	Wed, 27 Aug 2008 11:28:01 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Josh Triplett <josht@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, cl@...ux-foundation.org,
	mingo@...e.hu, akpm@...ux-foundation.org, manfred@...orfullife.com,
	dipankar@...ibm.com, schamp@....com, niv@...ibm.com,
	dvhltc@...ibm.com, ego@...ibm.com, laijs@...fujitsu.com,
	rostedt@...dmis.org
Subject: Re: [PATCH, RFC, tip/core/rcu] scalable classic RCU implementation

On Mon, Aug 25, 2008 at 05:26:43PM +0200, Peter Zijlstra wrote:
> On Mon, 2008-08-25 at 08:16 -0700, Paul E. McKenney wrote:
> > On Mon, Aug 25, 2008 at 12:34:56PM +0200, Peter Zijlstra wrote:
> > > On Fri, 2008-08-22 at 16:29 -0700, Josh Triplett wrote:
> > > 
> > > > > @@ -26,8 +27,10 @@
> > > > >   * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
> > > > >   *
> > > > >   * For detailed explanation of Read-Copy Update mechanism see -
> > > > > - * 		Documentation/RCU
> > > > > - *
> > > > > + * 	Documentation/RCU
> > > > > + * 	http://lwn.net/Articles/262464/ (What is RCU, Fundamentally?)
> > > > > + * 	http://lwn.net/Articles/263130/ (What is RCU's Usage?)
> > > > > + * 	http://lwn.net/Articles/264090/ (What is RCU's API? + references)
> > > > >   */
> > > > 
> > > > Why put these references here rather than in Documentation/RCU?  It
> > > > seems easier to keep documentation up to date in one place.  If you
> > > > think these represent a good "getting started" set of documents, how
> > > > about a Documentation/RCU/ReadTheseFirst with links to them, or how
> > > > about linking to them from whatisRCU.txt?
> > > 
> > > I actually like in code comments and 'documentation' more than
> > > Documentation/ stuff. Mostly because Documentation/ is:
> > >  - far away from the code
> > >  - therefore, more easily bitrotted
> > >  - and easily forgotten
> > 
> > I know!!!
> > 
> > #ifdef JOSH_TRIPLETT
> >  * 	Documentation/RCU
> >  * 	http://lwn.net/Articles/262464/ (What is RCU, Fundamentally?)
> >  * 	http://lwn.net/Articles/263130/ (What is RCU's Usage?)
> >  * 	http://lwn.net/Articles/264090/ (What is RCU's API? + references)
> > #elif PETER_ZIJLSTRA
> >  * 	Documentation/RCU
> > #endif
> > 
> > (Sorry, couldn't resist!!!)
> 
> But but but, you got the cases the wrong way around.. ;-)

Good point...

#ifdef READER_LIKES_DOCUMENTATION_URLS_IN_COMMENTS
 * 	Documentation/RCU
 * 	http://lwn.net/Articles/262464/ (What is RCU, Fundamentally?)
 * 	http://lwn.net/Articles/263130/ (What is RCU's Usage?)
 * 	http://lwn.net/Articles/264090/ (What is RCU's API? + references)
#else
 * 	Documentation/RCU
#endif

Of course, the C preprocessor would just remove the whole comment
anyway, but hopefully it is the thought that counts.  ;-)

> > Seriously, I know where all the documentation is, as I wrote most of it.
> > These comments are for you guys.  So, any thoughts on how I should
> > resolve this?  My default is, as always, a coin flip.  ;-)
> 
> I guess we could do the 'this is how the concept works and can be used
> like so and so' documentation in Documentation/

Documentation/RCU/whatisRCU.txt does in fact contain the three URLs
listed above.  And there is always Documentation/RCU/RTFP.txt for
people wanting the full effect.

> And the stuff that says 'this code does like so and so, because blah'
> should stay near the code.
> 
> And in any case of doubt - stay near the code :-)
> 
> I always view Documentation/ as end user stuff (be that a kernel
> programmer that needs to learn a new API, or userland folks or people
> wanting to know what a certain feature is about).

I confess to erring on the side of spamming all channels.  Then again,
I am a serial junk-mailer, so perhaps this is just me.

							Thanx, Paul
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