linux-kernel - Re: [PATCH RFC tip/core/rcu 32/41] rcu: Update stall-warning documentation

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Message-ID: <20120203055821.GD2380@linux.vnet.ibm.com>
Date:	Thu, 2 Feb 2012 21:58:21 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Josh Triplett <josh@...htriplett.org>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, niv@...ibm.com, tglx@...utronix.de,
	peterz@...radead.org, rostedt@...dmis.org, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH RFC tip/core/rcu 32/41] rcu: Update stall-warning
 documentation

On Thu, Feb 02, 2012 at 09:42:58PM -0800, Josh Triplett wrote:
> On Thu, Feb 02, 2012 at 10:18:05AM -0800, Paul E. McKenney wrote:
> > On Wed, Feb 01, 2012 at 09:56:39PM -0800, Josh Triplett wrote:
> > > On Wed, Feb 01, 2012 at 11:41:50AM -0800, Paul E. McKenney wrote:
> > > > From: "Paul E. McKenney" <paul.mckenney@...aro.org>
> > > > 
> > > > Add documentation of CONFIG_RCU_CPU_STALL_VERBOSE, CONFIG_RCU_CPU_STALL_INFO,
> > > > and RCU_STALL_DELAY_DELTA.  Describe multiple stall-warning messages from
> > > > a single stall, and the timing of the subsequent messages.  Add headings.
> > > 
> > > Don't some of these documentation changes go with earlier patches in
> > > this series?
> > 
> > Some could, but there is a fair amount of catch-up here.  Since we don't
> > need documentation to be bisectable, it makes sense to do a single
> > commit to update the documentation.
> 
> I think we've actually had this particular conversation once for each of
> the last few rounds of patches. :)
> 
> I agree that documentation doesn't have to allow bisection, but I do
> think it generally makes sense to add documentation together with
> whatever change it documents whenever possible.  Among other things,
> doing so makes a series of patches much easier to rearrange and merge.
> 
> When documenting things that previously had no documentation, and didn't
> appear in the same patch series, it makes sense to have a separate
> commit to add documentation.  I'd just suggest that when documenting
> things added or changed in the same patch series, the documentation
> should go with the addition or change.

And I did do that for several of the patches -- my new-found KVM testing
capability makes it much more convenient to do that.  But if I see that
a documentation file is a year or so behind, I don't feel obligated to
backport pieces of the changes to previous patches that happened recently
enough to not yet be in -tip.

							Thanx, Paul

> > > Also, this commit message doesn't say anything about the removal of
> > > RCU_SECONDS_TILL_STALL_RECHECK:
> > > 
> > > > --- a/Documentation/RCU/stallwarn.txt
> > > > +++ b/Documentation/RCU/stallwarn.txt
> > > > @@ -14,12 +14,36 @@ CONFIG_RCU_CPU_STALL_TIMEOUT
> > > >  	issues an RCU CPU stall warning.  This time period is normally
> > > >  	ten seconds.
> > > >  
> > > > -RCU_SECONDS_TILL_STALL_RECHECK
> > > [...]
> > > > -	This macro defines the period of time that RCU will wait after
> > > > -	issuing a stall warning until it issues another stall warning
> > > > -	for the same stall.  This time period is normally set to three
> > > > -	times the check interval plus thirty seconds.
> > 
> > It is now computed from CONFIG_RCU_CPU_STALL_TIMEOUT, which has an old
> > value for default, which is now fixed.  I will add the rationale for
> > removing CONFIG_RCU_SECONDS_TILL_STALL_RECHECK to the commit message.
> 
> Thanks.
> 
> - Josh Triplett
> 

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