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From Steve Loughran <ste...@apache.org>
Subject Re: Ant build slower on two cores than on one core?
Date Thu, 13 Mar 2008 17:12:39 GMT
Michael Meyer wrote:


> On mere build servers running linux one could disable
> the second core at boot time permanently to reduce the
> build time, if no other processes are running on this
> server.
> 
> But on workstations the second core is often used by
> the application being developed if it is
> multithreaded, so there might be no way in linux to
> reduce the build time wih two cores?


we dont want to turn core #2, off, or even cores #3 and #4. Not when my 
memory/process footprint has 3 vmware images (windows for exchange, 
centos for release builds, rhel4 for testing and then the IDE on my main 
machine)


   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND 

  9184 slo       18   0 2443m 802m  15m S    0 13.4  84:51.39 java 

  9129 slo        5 -10  770m 579m 561m S    0  9.7  38:32.89 vmware-vmx 

  8403 slo        5 -10  768m 570m 556m S   16  9.5 850:09.04 vmware-vmx 

  8361 slo       15   0  891m 368m  29m S    2  6.2  63:29.62 
firefox-bin
  9144 slo        5 -10  501m 304m 290m S    0  5.1   6:12.59 vmware-vmx 

  8253 slo       15   0  373m 251m  22m S    0  4.2  12:02.73 
thunderbird-bin
29911 slo       18   0 1641m 177m  12m S    0  3.0   7:42.59 java 

  5708 root      15   0  314m 167m  59m S    0  2.8  30:08.87 Xorg 

24284 slo       17   0 1560m 141m 8692 S    0  2.4   0:35.69 java 

19907 slo       15   0  645m  92m  61m S    0  1.6   0:04.22 soffice.bin 

11023 slo       15   0  609m  69m  36m S    0  1.2  22:51.60 amarokapp 

  8304 slo       15   0  384m  54m  28m S    0  0.9   1:47.77 vmware

I had a look at the code and there's no obvious synchronisation in the 
javac code. If there is a delay, it may be in the output/listener logic, 
which could well be synchronized. On a multicpu system the cost of 
acquiring a lock may be higher.

I'd love to track this down, but nothing obvious springs to mind.

-could you try building under vmware/xen? We do that for releases to 
ensure the release builds are with clean source, no matter what I'm editing.

-steve

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