Roman Leshchinskiy wrote:
Currently, with recursive make, this means we jump around between
Makefiles a lot, which isn't good for parallelism in the build.
Instead, we want to move all the logic and dependencies into the root
Makefile (or files that get included into it) so that make sees all of
it together.
Does this mean that you want to have one giant Makefile which build all
of GHC, including all libraries? Why? Is it only to be able to build
several packages in parallel? IMO, the disadvantages of this far
outweigh this modest benefit.
The standard citation is "Recursive make considered harmful" by Peter Miller:
http://miller.emu.id.au/pmiller/books/rmch/?ref=DDiyet.Com
I should say up front that I'm not completely sure this is going to work
out, which is one reason we need to try it on a branch. But the approach
has the potential to improve things a lot:
* we get to specify dependencies between different parts of the tree much
more easily and precisely. BIG WIN. Have you noticed how often you
need to 'make distclean' in a GHC tree to make sure everything is up to
date? (well I rarely do this, because I have the dependencies in my
head and I can rebuild manually, but I imagine this isn't the case for
most people!)
* we get more parallelism, more easily. I'd argue this is a big win too,
right now a validate only uses about 1.3 out of 2 cores.
We don't lose modularity: different parts of the build system are still in
different files, it's just that make sees them all at once. Right now
every make invocation already reads thousands of lines of boilerplate
Makefile code, and we'd be invoking make only once rather than many times.
So we will probably have to worry about efficiency. For example, it takes
tens of seconds on Windows for make to discover that compiler/ is up to
date. We don't want that happening every time you rebuild some small part
of the tree, so we plan to cut a few dependencies on purpose. But I'm
hoping it'll be necessary to do this in a few well-defined places only, and
only when building in subdirectories. For example, If you say 'make' in
libraries/base, then we won't try to rebuild the stage1 compiler, we'll
just fail if it does't exist.
Cheers,
Simon
_______________________________________________
Cvs-ghc mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/cvs-ghc
