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Re: [Wireshark-commits] rev 49995: /trunk/ /trunk/: macosx-setup.sh
From: Dirk Jagdmann <doj () cubic org>
Date: Tue, 18 Jun 2013 12:01:06 -0700

How many processor cores does your machine have, and are they multi-threaded?

I have a 4-dual-threaded-core machine (and a solid-state disk and a lot of memory), and "-j 8" seems to run the CPU at about 100%.  I don't 
know whether "number of threads" would be a good default in all cases - what you really want is to keep cranking up the number of jobs until 
things don't get faster, but that's a pain - but, if it is a good default, then

        sysctl -n hw.logicalcpu

would give cores*threads-per-core (tested on Snow Leopard, Lion, and Mountain Lion; the script doesn't work on Leopard, as 
the versions of at least some of the software won't configure and build, and I gave up trying to make them build).

(I originally used -j 4, but then saw something about a multi-threaded version of the IBM System/360 Model 195 that 
noted that multi-threading can help deal with pipeline bubbles due to unpredicted or mispredicted branches, so I tried 
-j 8 and found the CPU was busier than with -j 4.)

hmm, there are many points discussed here:

- do we want to make a smart decision on the number of parallel make jobs, possibly derived from the number of cores?

My personal opinion is yes. On OsX using the sysctl mentioned by Guy is probably a good starting point. Adding my own experience you'll want to oversubscribe the number of jobs over the number of cores a little bit, so that when jobs are waiting for I/O action another job can use the free CPU. With my personal experience calculating something like "number of cores"*1.5 seems reasonable, because if you're waiting for the long lasting build job on your desktop computer, you want some "juice" left over for web browsing, email reading or whatever. (This applies to all modern operating system, Windows, Linux, OsX)

- the other question is, which versions of OsX are we targetting for developer support going forward. Personally I think no serious Wireshark user will use an earlier version of OsX than 10.6, so we should be safe.

(personal note, my old MacBook Pro has two cores and no hyper-thread, so personally I'm fine with 3 make jobs [note that this was the default in the OsX build script for a long time])

---> Dirk Jagdmann
----> http://cubic.org/~doj
-----> http://llg.cubic.org
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