On 6/4/07, Greg Schafer <[EMAIL PROTECTED]> wrote: > Deskin Miller wrote: > > > Is this worth adding to the book? > > Most definitely IMHO. Multi-core systems will soon be the norm. It's just > crazy not to take advantage. There used to exist a "SMP" hint somewhere. > Maybe this is it: > > http://www.linuxfromscratch.org/hints/downloads/files/OLD/parallelcompiling.txt > > A lot of seasoned SMP-building folks work on the basis of make -j X+1 ie: > make -j3 if you have 2 cpus or 2 cores. As a person who has been building > in parallel for a long time, I strongly disagree with a comment elsewhere > in this thread about performance plummeting if overutilizing.
I completely agree with what you're saying and I've been using j3 for quite a while now on a dual core. It's much faster and performance doesn't plummet, AFAIK. Basically, just how much load do you want to put on the cpu? If you have two cpus, eight jobs, and they each use 25% of a single CPU, I don't know if that will finish in less time than two jobs maxing out each CPU. I'm still not sure it deserves a spot in _this_ book, though since we don't even point out the gcc optimizations, either. Anyone with a whiff of experience is going to know about using parallel jobs in make. But... > The gotcha with this approach is *ALL* invocations of `make' are affected, > even those for `make install'. This can lead to some interesting failures. > But it's easy enough to work around, just add `-j1' to the "known-to-fail" > cases. Exactly. You're counting on the Makefile to have well constructed dependencies. With most automaked projects, this is taken care of unless there are also custom rules in Makefile.am. In non-automaked projects, you can almost guarantee that make will race. It would suck to have a bunch of noob questions about broken builds because of this. You make a good point, though, about the simplicity of the workaround. Possible text to appear at an unknown location in the LFS book: "The `make' utility allows multiple jobs to be run simultaneously when building packages. This can allow a significant speed increase on multiple processor systems. This is controlled by passing the -j<jobs> option to `make'. For instance, you might execute `make -j2 install' on a dual-core system. The problem with this approach is that it depends on a well written Makefile to support multiple simultaneous jobs. If there is a build error, it is important to remove the jobs option to ensure that this is not the cause of the error." -- Dan -- http://linuxfromscratch.org/mailman/listinfo/lfs-dev FAQ: http://www.linuxfromscratch.org/faq/ Unsubscribe: See the above information page
