Re: [PATCH v3 3/8] coccicheck: enable parmap support

["Luis R. Rodriguez" <mcgrof@kernel.org>]

On Tue, Jun 21, 2016 at 11:44:09PM +0200, Julia Lawall wrote:
> 
> 
> On Tue, 21 Jun 2016, Luis R. Rodriguez wrote:
> 
> > On Tue, Jun 21, 2016 at 11:32:11PM +0200, Julia Lawall wrote:
> > > 
> > > 
> > > On Tue, 21 Jun 2016, Luis R. Rodriguez wrote:
> > > 
> > > > On Tue, Jun 21, 2016 at 11:00:53PM +0200, Nicolas Palix (LIG) wrote:
> > > > > Hi,
> > > > > 
> > > > > Le 21/06/16 à 22:43, Julia Lawall a écrit :
> > > > > >
> > > > > >
> > > > > >On Tue, 21 Jun 2016, Luis R. Rodriguez wrote:
> > > > > >
> > > > > >>On Tue, Jun 21, 2016 at 10:17:38PM +0200, Julia Lawall wrote:
> > > > > >>>
> > > > > >>>
> > > > > >>>On Tue, 21 Jun 2016, Luis R. Rodriguez wrote:
> > > > > >>>
> > > > > >>>>Coccinelle has had parmap support since 1.0.2, this means
> > > > > >>>>it supports --jobs, enabling built-in multithreaded functionality,
> > > > > >>>>instead of needing one to script it out. Just look for --jobs
> > > > > >>>>in the help output to determine if this is supported.
> > > > > >>>>
> > > > > >>>>Also enable the load balancing to be dynamic, so that if a
> > > > > >>>>thread finishes early we keep feeding it.
> > > > > >>>>
> > > > > >>>>Note: now that we have all things handled for us, redirect stderr to
> > > > > >>>>stdout as well to capture any possible errors or warnings issued by
> > > > > >>>>coccinelle.
> > > > > >>>>
> > > > > >>>>If --jobs is not supported we fallback to the old mechanism.
> > > > > >>>>This also now accepts DEBUG_FILE= to specify where you want
> > > > > >>>>stderr to be redirected to, by default we redirect stderr to
> > > > > >>>>/dev/null.
> > > > > >>>
> > > > > >>>Why do you want to do something different for standard error in the parmap
> > > > > >>>and nonparmap case?
> > > > > >>
> > > > > >>We should just deprecate non-parmap later.
> > > > > >
> > > > > >that's not really getting at the point.  I like the DEBUG_FILE= solution.
> > > > > >I don't like merging stderr and stdout.  So you've put what to my mind is
> > > > > >the good solution only in the deprecated case (to my understanding of
> > > > > >the commit message).
> > > > > 
> > > > > I agree. You're not just "enabling parmap support". You're
> > > > > also changing how messages to stderr are handled.
> > > > > Maybe add the DEBUG_FILE mechanism in a separate patch for both
> > > > > modes (parmap and non-parmap).
> > > > 
> > > > I'd prefer to just rip out non-parmap support and bump coccinelle
> > > > requiremetns to at least 1.0.3, thoughts?
> > > 
> > > There are already too many changes in this patch series.
> > > 
> > > Also, I don't know what the 0-day people would find convenient.
> > 
> > I'd really prefer to not deal with supporting DEBUG_FILE  for non-parmap
> > case due to the way parallelism is supported there, it uses wait(1) to
> > wait on the shell, and for spawning this nasty thing:
> > 
> > eval "$@ --max $NPROC --index $i &"
> > 
> > Specially since we are likely to be able to deprecate this sooner
> > rather than later I see little point in adding DEBUG_FILE into this
> > mess.
> 
> Sorry, I didn't realize there was parallelism without parmap. 

Yea :( so is the change OK as-is then, only I need to update the commit log?

> My thought 
> was that if someone is running Coccinelle on only one core, then why force 
> them to use parmap.

Oh but that's different feedback. Sure, but why should that be an issue ?
It would seem that coccinelle would just do the right thing with -j 1 used.

> Coccinelle could of course be updated to not use 
> parmap when the number of cores is 1.

:) Single CPU systems are probably odd bests these days, either way I can
update the script to avoid parmap if number of cpus is 1 since I'm respinning.

  Luis