Re: Distributed Build not any faster
Re: Distributed Build not any faster
- Subject: Re: Distributed Build not any faster
- From: Chris Espinosa <email@hidden>
- Date: Fri, 13 Feb 2009 19:21:57 -0800
On Feb 13, 2009, at 6:54 PM, Wes Plate wrote:
Today I set up for my programmers two new 8-core Mac Pros (now there
are
three OctoMacs) so we wanted to see how must distributed builds
speed things
up. All three Mac Pros are running the latest OS (OS X client
10.5.6) and
Xcode 3.1.2 and during the build all three systems are working, you
can see
their CPUs go to work in Activity Monitor. But the results weren't
impressive, a build that took about 5 minutes on a single machine
took about
5 minutes on all three.
The network is Gigbit ethernet and is generally quite speedy.
Are distributed builds just not worth it in these days of multi-core
Macs,
or is there something we need to do to see real speed gains?
Distributed Builds were first introduced in the era of dual-core
PowerPC machines, where network and disk I/O speeds were sufficiently
faster than compute power that the cost of distributing jobs over the
network was more than made up for by the fan-out of having more CPUs
working on source.
With 8 cores running at 3GHz each, with big L2 and L3 caches and
direct connections to the bus, a modern Mac Pro will almost always be
faster doing a local build than a distributed build, except in cases
where it's so memory-starved that it ends up swapping.
Distribution gives the best gains when distributing from a slow
machine with a good network to 3 or 4 similar-speed machines (using
Dedicated Network Builds, up to 8 or 10). It is pretty much a wash
when distributing from reasonably powerful machines to their peers,
and it is a net loss when distributing from a fast machine to a
network of slower ones, as the transmission costs far exceed the
computational gains.
Note also that small Objective-C files compile pretty fast nowadays,
and that much of your build time ends up being linking and resource
copying (which can't be distributed). Distributed builds are a much
bigger win for large C++ files, which are more computationally-intense
for the compiler.
Chris
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