Re: [PATCH 4/4] coccicheck: add indexing enhancement options

[Luis R. Rodriguez]

On Fri, Jun 10, 2016 at 11:21:28PM +0200, Julia Lawall wrote:
> 
> 
> On Fri, 10 Jun 2016, Luis R. Rodriguez wrote:
> 
> > On Fri, Jun 10, 2016 at 11:02:38PM +0200, Julia Lawall wrote:
> > > 
> > > 
> > > On Fri, 10 Jun 2016, Luis R. Rodriguez wrote:
> > > 
> > > > Enable indexing optimizations heuristics. Coccinelle has
> > > > support to make use of its own enhanced "grep" mechanisms
> > > > instead of using regular grep for searching code 'coccigrep',
> > > > in practice though this seems to not perform better than
> > > > regular grep however its expected to help with some use cases
> > > > so we use that if you have no other indexing options in place
> > > > available.
> > > > 
> > > > Since git has its own index, support for using 'git grep' has been
> > > > added to Coccinelle, that should on average perform better than
> > > > using the internal cocci grep, and regular grep. Lastly, Coccinelle
> > > > has had support for glimpseindex for a long while, however the
> > > > tool was previously closed source, its now open sourced, and
> > > > provides the best performance, so support that if we can detect
> > > > you have a glimpse index.
> > > > 
> > > > These tests have been run on an 8 core system:
> > > > 
> > > > Before:
> > > > 
> > > > $ export COCCI=scripts/coccinelle/free/kfree.cocci
> > > > $ time make coccicheck MODE=report
> > > > 
> > > > Before this patch with no indexing or anything:
> > > > 
> > > > real    16m22.435s
> > > > user    128m30.060s
> > > > sys     0m2.712s
> > > > 
> > > > Using coccigrep (after this patch if you have no .git):
> > > > 
> > > > real    16m27.650s
> > > > user    128m47.904s
> > > > sys     0m2.176s
> > > > 
> > > > If you have .git and therefore use gitgrep:
> > > > 
> > > > real    16m21.220s
> > > > user    129m30.940s
> > > > sys     0m2.060s
> > > > 
> > > > And if you have a .glimpse_index:
> > > > 
> > > > real    16m14.794s
> > > > user    128m42.356s
> > > > sys     0m1.880s
> > > 
> > > I don't see any convincing differences in these times.
> > > 
> > > I believe that Coccinelle's internal grep is always used, even with no 
> > > option.
> > 
> > Ah that would explain it. This uses coccinelle 1.0.5, is the default
> > there to use --use-coccigrep if no other index is specified ?
> 
> It has been the default for a long time.
> 
> > > I'm puzzled why glimpse gives no benefit.
> > 
> > Well, slightly better.
> 
> No, it should be much better.  You would have to look at the standard 
> error to see if you are getting any benefit.  There should be very few 
> occurrences of Skipping if you are really using glimpse.  In any case, if 
> you asked for glimpse and it was not able to provide it, there should be 
> warning messages at the top of stderr.

I'll redirect stderr to stdout by default when parmap support is used then.

  Luis