Re: Distributed build overhead and Mac Mini vs XServe pricing
Re: Distributed build overhead and Mac Mini vs XServe pricing
- Subject: Re: Distributed build overhead and Mac Mini vs XServe pricing
- From: Mark Dawson <email@hidden>
- Date: Mon, 17 Jan 2005 08:05:16 -0800
It's too bad that RAM disks are not supported on OS X--adding 1 GB of
memory to a G5 is less than $150. If I/O disk speed is important,
having 1 GB of memory, instead of a drive, should be a lot faster
(back in the olden days of OS 7, I remember adding a RAM disk could
speed up MPW C++ compiles by 2x, and even with OS 9/G4s, by up to
40%).
It was pointed out that RAM disks ARE supported. However, in a simple
test, they gave no benefit.
I set up a 128 MB RAM disk, and copied the "Sketch" example program
over, along with the XCode application itself, and the Frameworks that
are linked (Cocoa, AppKit, Foundation). I launched Activity Monitor,
and at no time during the build process did "Free Memory" get less than
300 MB (I have 1.5 GB installed). In the RAM disk project, I pointed
the frameworks (cmd-I, choose) to the RAM disk frameworks. This
project creates a precompiled header. This was running on a dual 1 GHz
G4 with 1.5 GB memory and 10.3.7, with the XCode 1.5 developer tools
installed.
Steps:
(1a) Launch XCode & project from RAM disk
(1b) Launch XCode & project from 7200 RPM UATA 133 drive (boot 10.3.7
drive)
(2) Do a "clean all targets"
(3) Build
Results:
RAM Disk: 16.4 seconds
Hard drive: 15.6 seconds
Multiple runs showed about the same result (hard drive beating the RAM
disk by a few tenths of a second).
Maybe this sample project is too simple (too short), but it seems to
rule out file I/O as a big factor (at least in relation to already
existing RAM). Given that "Free Memory" never got less than 300 MB,
I'm assuming that my RAM disk didn't cause any excess page faults, so
it was a "fair" test. It would seem that OS X's disk cache negates any
negative speed differential of a hard drive.
That could mean that the Mac mini's 4200 RPM drive wouldn't be a factor
if only XCode and its tools were running (i.e., there was enough memory
for the disk cache to handle all I/O).
Mark
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