21 Feb
2012
21 Feb
'12
7 p.m.
On 21/02/12 1:23 PM, Dave McGuire wrote:
On 02/21/2012 08:30 AM, Toby Thain wrote:
I've *only* ever seen a superlinear speedup on parallel builds. Are your
Makefiles ok?
Yes, I know how to write correct Makefiles.
By superlinear I mean, taking less time than the serialised process
divided by the number of cores, which is what Sean is seeing. I am not
sure I've ever seen this. Close to 1/N, sure. But 0.7/N?
--Toby
Not an
embedded system, but at work we have access to a multicore SPARC
system (Sun, I don't recall the model since it's actually stashed away
in a
data center) with 8 cores. Doing a parallel make (it helps to have a
properly written makefile; I went to the trouble to do so for the part
I'm
responsible for) only takes 1/10th the time of a non-parallel make.
Impressive. I've yet to see a *super*linear speedup for parallel make,
myself.
--Toby (uses 8 core at work)
Actually there's one exception: running under SunOS 4. That was ages ago
of course. It did SMP, but only one CPU can be in the kernel at once
(one big lock!) so system calls were a big bottleneck.
-Dave