On Nov 13, 2006, at 21:27, Dave Korn wrote:
To be fair, Mike was talking about multi-core SMP, not threading
on a single
cpu, so given that CPU usage is at 100% now for most jobs, there is
an Nx100%
speedup to gain from using 1 thread on each of N cores.
I'm mostly building GCC on multiprocessor CPUs and typically
run make -j (number_of_processors + 1).
The main place where threading may make sense, especially
with LTO, is the linker. This is a longer lived task, and
is the last step of compilation, where no other parellel
processes are active. Moreover, linking tends to be I/O
intensive, so a number of threads will likely be blocked
for I/O.
I'm not really sure how this would play with SMP (as opposed to
threading).
I don't see why you think threading could be particularly useful in
the
linker? It's the pipeline of compiler optimisation passes that
looks like an
obvious candidate for threading to me.
This would be when we do link-time optimizations. These optimizations
will be on much larger datasets and occur when with no work remaining
to do in parallel.
-Geert
