Messages in this thread | | | Date | Wed, 22 Jun 2016 17:10:24 +0200 | From | "Luis R. Rodriguez" <> | Subject | Re: [Cocci] [PATCH v3 3/8] coccicheck: enable parmap support |
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On Wed, Jun 22, 2016 at 07:25:11AM +0200, Julia Lawall wrote: > > > On Wed, 22 Jun 2016, Luis R. Rodriguez wrote: > > > 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. > > Some semantic patches have to be run single core, eg due to the use of > finalize. Perhaps there would be some reason to run them single core, if > one had the same nmber of semantic patches as cores. This was more > relevant before dynamic load balancing though. Single core is also better > when using an option that takes a lot of include files and when using > --include-headers-for-types. Then one has maximal sharing of include file > information across the treatment of the different C files. In contrast, > chunksize 1 is worst. In that case, there is no effective caching of > parsed header files, because Coccinelle has no shared memory.
I've disabled parmap for 1 CPU now.
> Actually, it would be probably good to raise the default chunksize a bit > for the latter reason. It would depend on which files get assigned to > which chunks though how much benefit it might have.
What value do you have in mind? Or should we leave this as a separate future change?
Luis
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