Re: PBXNumberOfParallelBuildSubtasks and Xcode4
Re: PBXNumberOfParallelBuildSubtasks and Xcode4
- Subject: Re: PBXNumberOfParallelBuildSubtasks and Xcode4
- From: Andreas Grosam <email@hidden>
- Date: Thu, 21 Apr 2011 11:01:05 +0200
On Apr 20, 2011, at 8:47 PM, Joar Wingfors wrote:
>
> On 20 apr 2011, at 01.52, Serge MONTAIGU wrote:
>
>> Thank you for IDEBuildOperationMaxNumberOfConcurrentCompileTasks !!!
>> Setting this number to 12 speeds up the compile time dramatically (from 40 mn to 4 mn !!) but I will buy more memory to upgrade my machine to 16Gb.
>
>
> Please note that "virtual CPUs" are less efficient than physical CPUs. You'll probably see a bit of performance improvement if you add enough RAM to run 24 concurrent compiles, but don't expect it to be anywhere near 2x. The money *might* be better spent on an SSD. If you can benchmark ahead of time, try it out before you commit to getting the additional RAM. Just as a FYI.
>
> That said, getting more RAM is almost always a good decision...
On my MacBookPro5,1 with 4GB RAM installed, compiling a one file C++ console app which includes a bunch of boost headers, and a prefix header this happens:
PID COMMAND %CPU TIME #TH #WQ #POR #MREG RPRVT RSHRD RSIZE
16355 clang 38.5 00:10.49 1/1 0 14 704 882M+ 11M 1094M+
16357 clang 97.3 00:04.11 1/1 0 14 729+ 530M+ 6928K+ 707M+
15669 Xcode 0.4 86:40.93 16 10 261- 973- 91M- 67M 242M-
That is, Xcode spawns two clang processes. Due to this, the Free Mem goes to nearly zero and the system stalls. Compiling this including compiling the prefix header takes roughly 50 seconds (measured watching the system clock in the menu bar, so not terrible accurate).
Launching clang on the console, even when Xcode is running at 100%, trying desperately to index and consuming lots of mem and CPU,
PID COMMAND %CPU TIME #TH #WQ #POR #MREG RPRVT RSHRD RSIZE
15669 Xcode 99.8 01:41:47 14/1 7 241 1323+ 476M+ 67M 881M+
this takes:
$ time /Xcode4/usr/bin/llvm-g++ -arch x86_64 main.cpp -o test -I/opt/local/include
real 0m7.777s
user 0m6.896s
sys 0m0.708s
That is, it takes about 8 seconds.
So, good to know about IDEBuildOperationMaxNumberOfConcurrentCompileTasks. :/
Yes, clang and Xcode is truly awesome, but still needs a lot of polish (and a couple of fixes).
Will file a bug report with a bunch of more info.
Regards
Andreas _______________________________________________
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