Hi, I have some news. :-)
I replicated the Martin Liška experiment [1] on a 64-cores machine for
gcc [2] and Linux kernel [3] (Linux kernel was fully parallelized),
and I am excited to dive into this problem. As a result, I want to
propose GSoC project on this issue, starting with something like:
1- Systematically create a benchmark for easily information
gathering. Martin Liška already made the first version of it, but I
need to improve it.
2- Find and document the global states (Try to reduce the gcc's
global states as well).
3- Define the parallelization strategy.
4- First parallelization attempt.
I also proposed this issue as a research project to my advisor and he
supported me on this idea. So I can work for at least one year on
this, and other things related to it.
Would anyone be willing to mentor me on this?
[1] https://gcc.gnu.org/bugzilla/attachment.cgi?id=43440
[2] https://www.ime.usp.br/~belinass/64cores-experiment.svg
[3] https://www.ime.usp.br/~belinass/64cores-kernel-experiment.svg
On Mon, Nov 19, 2018 at 8:53 AM Richard Biener
wrote:
>
> On Fri, Nov 16, 2018 at 8:00 PM Giuliano Augusto Faulin Belinassi
> wrote:
> >
> > Hi! Sorry for the late reply again :P
> >
> > On Thu, Nov 15, 2018 at 8:29 AM Richard Biener
> > wrote:
> > >
> > > On Wed, Nov 14, 2018 at 10:47 PM Giuliano Augusto Faulin Belinassi
> > > wrote:
> > > >
> > > > As a brief introduction, I am a graduate student that got interested
> > > >
> > > > in the "Parallelize the compilation using threads"(GSoC 2018 [1]). I
> > > > am a newcommer in GCC, but already have sent some patches, some of
> > > > them have already been accepted [2].
> > > >
> > > > I brought this subject up in IRC, but maybe here is a proper place to
> > > > discuss this topic.
> > > >
> > > > From my point of view, parallelizing GCC itself will only speed up the
> > > > compilation of projects which have a big file that creates a
> > > > bottleneck in the whole project compilation (note: by big, I mean the
> > > > amount of code to generate).
> > >
> > > That's true. During GCC bootstrap there are some of those (see PR84402).
> > >
> >
> > > One way to improve parallelism is to use link-time optimization where
> > > even single source files can be split up into multiple link-time units.
> > > But
> > > then there's the serial whole-program analysis part.
> >
> > Did you mean this: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84402 ?
> > That is a lot of data :-)
> >
> > It seems that 'phase opt and generate' is the most time-consuming
> > part. Is that the 'GIMPLE optimization pipeline' you were talking
> > about in this thread:
> > https://gcc.gnu.org/ml/gcc/2018-03/msg00202.html
>
> It's everything that comes after the frontend parsing bits, thus this
> includes in particular RTL optimization and early GIMPLE optimizations.
>
> > > > Additionally, I know that GCC must not
> > > > change the project layout, but from the software engineering
> > > > perspective,
> > > > this may be a bad smell that indicates that the file should be broken
> > > > into smaller files. Finally, the Makefiles will take care of the
> > > > parallelization task.
> > >
> > > What do you mean by GCC must not change the project layout? GCC
> > > happily re-orders functions and link-time optimization will reorder
> > > TUs (well, linking may as well).
> > >
> >
> > That was a response to a comment made on IRC:
> >
> > On Thu, Nov 15, 2018 at 9:44 AM Jonathan Wakely
> > wrote:
> > >I think this is in response to a comment I made on IRC. Giuliano said
> > >that if a project has a very large file that dominates the total build
> > >time, the file should be split up into smaller pieces. I said "GCC
> > >can't restructure people's code. it can only try to compile it
> > >faster". We weren't referring to code transformations in the compiler
> > >like re-ordering functions, but physically refactoring the source
> > >code.
> >
> > Yes. But from one of the attachments from PR84402, it seems that such
> > files exist on GCC,
> > https://gcc.gnu.org/bugzilla/attachment.cgi?id=43440
> >
> > > > My questions are:
> > > >
> > > > 1. Is there any project compilation that will significantly be improved
> > > > if GCC runs in parallel? Do someone has data about something related
> > > > to that? How about the Linux Kernel? If not, I can try to bring some.
> > >
> > > We do not have any data about this apart from experiments with
> > > splitting up source files for PR84402.
> > >
> > > > 2. Did I correctly understand the goal of the parallelization? Can
> > > > anyone provide extra details to me?
> > >
> > > You may want to search the mailing list archives since we had a
> > > student application (later revoked) for the task with some discussion.
> > >
> > > In my view (I proposed the thing) the most interesting parts are
> > > getting GCCs global state documented and reduced. The parallelization
> > > itself is an interesting experiment but whether there will be any
>
