On Fri, Aug 30, 2013 at 5:37 PM, Iustin Pop <[email protected]> wrote: > On Fri, Aug 30, 2013 at 10:28:25AM +0200, Jose A. Lopes wrote: >> Hi, >> >> I took another look at the Makefile regarding this problem and I think >> there are 3 use cases to focus on. These uses cases concern partial >> compilation of Haskell sources, i.e., I have compiled some Haskell >> sources with some flags and other Haskell sources with other flags, >> and I don't want to mix different flags in the same linkage stage. >> >> The three uses cases are: >> 1. Normal compilation >> 2. Compilation with profiling >> 3. Compilation with coverage >> >> This means, for example, that we shouldn't mix Haskell object files >> compiled with profiling with those compiled with coverage. >> >> There are other flags that control Haskell compilation, such as, PCRE >> and Parallel3, that control whether these libraries are available. >> However, these seem less important in the following sense: they are >> defined at configure time and they should remain the same while >> compiling the Haskell binaries. In other words, I don't thinkg that >> we should worry about someone compiling some Haskell source files with >> PCRE and some other Haskell source files without PCRE. The same for >> Parallel3. > > Indeed. > >> Anyone care to comment ? > > I have only one question, in general: what is the goal you're trying to > achieve? > > If it is to eliminate duplicate compilation of the same source file, I > have two notes to make (and I won't comment more on this thread): > > - even if files are compiled twice or N times, you have many CPUs, so > you're not blocked on it; what's the problem with having 3 CPUs all > compiling the same file?
On many machines where we compile ganeti (including: external buildbot instances, developers' laptops, other virtual machines) there are not "that many" cpus, or not that many to dedicate to totally parallel compilation. Reducing the compile time I think is worthwhile (if we don't break functionality) and is going to make people life better. > - the proper way to eliminate duplicate compilation, if you really want > it, is to simulate/duplicate what Cabal does: build once all files in > a local package, then link the binaries against the (single, common) > library; this way, all issues will go away > > Doing more Makefile-style work seems to me more worth than trouble. > Ok. But wouldn't that allow the "library" to be compiled with only one flag (eg. with or without profiling, coverage, and with one single value for any ifdefs?). If so how is this an improvement over compiling everything just once (without the suffixes for each binary?). (Maybe I'm missing something, here) Thanks, Guido
