Ashley Moran wrote:
Hi
I've read the following snippet out of the handbook hundreds of times and
still don't understand it. I even asked one of the developers I work with
and he was baffled too.
It is now possible to specify a -j option to make which will cause it to
spawn several simultaneous processes. This is most useful on multi-CPU
machines. However, since much of the compiling process is IO bound rather
than CPU bound it is also useful on single CPU machines.
What I want to know is, if compiling is IO bound, and you increase the number
of simultaneous processes compiling your world, where do the extra processes
get data from if the IO bandwidth is all used.
Have I misunderstood the term IO bound? Please help, I feel like a right
tool.
Just as a side line... does anybody know the best -j value to build world on a
4-core box?
The way I understand it is that 1 core would do this...
compile .... read disk .... compile .... read disk ... compile
It wont be reading when it is compiling and cant compile when its
reading so if you do -j 2 even on a single core machine it could do:
compile .... read disk .... complile .... read disk ... compile
read disk .... complile .... read disk ... compile .... read disk
Which means neither the CPU or the disks are idle resulting in faster
performance.
Cheers
Richard
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