On Tue, Nov 1, 2011 at 12:30 PM, Óscar Fuentes <ofv at wanadoo.es> wrote:> greened at obbligato.org (David A. Greene) writes: > >> Óscar Fuentes <ofv at wanadoo.es> writes: >> >>> A good measure of how fast a set of Makefile are is to run the build >>> with all targets up-to-date. Both builds takes a few seconds (3 or so) >>> on my Linux quad core box. Whatever improvement can be achieved on this >>> seems pretty insignifant. >> >> Oh, it's significant. When I build the Cray compiler with only non-LLVM >> stuff changed, the actual compiles (the Cray stuff) finish before the >> LLVM figures out nothing has changed. This is a sginificant >> productivity loss. > > How is that? Your compiler builds in less than 3 seconds? (IIRC, the > numbers are more like 1.5 seconds with a warm cache on a Linux 4core 2.4 > GHz machine) Maybe the LLVM build is starved because of your compiler's > build. > >> The Cray compiler uses a non-recursive make and so >> gets tons of parallelism the LLVM build simply can't see because it's >> recursive. > > There is no parallel loss due to recursive calls. The cmake build will > happily compile files from different libraries/executables as long as > there are enough threads available and no blocking dependencies. To > check, simply run `make -j' and you'll see how dozens of compiler > processes are started. AFAIR the same applies to the `make' build. > >>> Furthermore, recursive make is necessary for automatic generation of >>> header dependencies, among other things. The makefiles generated by >>> cmake are "partially" recursive for that reason: >> >> Eh? This is not true. See for example: >> >> http://mad-scientist.net/make/autodep.html > > LLVM/Clang uses a lot of generated headers. I think that what that page > says does not apply to our case.(Chromium's build system has to deal with several generated headers as well and uses a variant of the build system described on that page, without using recursive make as far as I know.) (Nico)
Óscar Fuentes
2011-Nov-01 20:04 UTC
[LLVMdev] [cfe-dev] RFC: Upcoming Build System Changes
Nico Weber <thakis at chromium.org> writes:>>>> Furthermore, recursive make is necessary for automatic generation of >>>> header dependencies, among other things. The makefiles generated by >>>> cmake are "partially" recursive for that reason: >>> >>> Eh? This is not true. See for example: >>> >>> http://mad-scientist.net/make/autodep.html >> >> LLVM/Clang uses a lot of generated headers. I think that what that page >> says does not apply to our case. > > (Chromium's build system has to deal with several generated headers as > well and uses a variant of the build system described on that page, > without using recursive make as far as I know.)Okay, we can get rid of recursive make. However, as pointed out elsewhere, removing recursive make will not make a difference on the LLVM build. What David Greene says probably is related to difference sizes among his compiler and LLVM.
David A. Greene
2011-Nov-01 22:09 UTC
[LLVMdev] [cfe-dev] RFC: Upcoming Build System Changes
Óscar Fuentes <ofv at wanadoo.es> writes:> Okay, we can get rid of recursive make. However, as pointed out > elsewhere, removing recursive make will not make a difference on the > LLVM build. What David Greene says probably is related to difference > sizes among his compiler and LLVM.Ok, whatever. I'm done arguing experiences. -Dave
Seemingly Similar Threads
- [LLVMdev] [cfe-dev] RFC: Upcoming Build System Changes
- [LLVMdev] [cfe-dev] RFC: Upcoming Build System Changes
- [LLVMdev] [cfe-dev] RFC: Upcoming Build System Changes
- [LLVMdev] [cfe-dev] RFC: Upcoming Build System Changes
- [LLVMdev] [cfe-dev] RFC: Upcoming Build System Changes