Hi,
nia wrote:
Has anyone benchmarked increasing numbers of make -jX on
single-processor systems with lots of memory?
Up until now, I've been operating under the assumption that
-j2 helps by not making the process wait on the file system
once the previous job is complete - but I wonder if that's
true at all...
that is an interesting question. I think it depends form a lot of
factors: what is being built, RAM available, compilers, file-system....
The old golden rule was to put N+1 where N is the number of CPUs/cores
availble.
OpenBSD guys said to restrain that to physical cores and not HT cores,
but in my experience that's wrong, given enough RAM.
I found that more jobs means more swap, so if you don't have plenty of
RAM and a very fast HDD, at the end, it gets worse, especially for
today's compilers with C++, meson and other that suck up until the last bit.
Worse of all is Rust.
So I keep jobs = N. cpus or in extreme cases even less for very big
programs. For a mix like pkgsrc I find it the best bet... if you have
one specific item building and rebuilding, you may try and time yourself.
In old times, with gcc 2.95, I found it convenient to add N+1!!
Riccardo
