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Old 07-23-2009, 05:51 AM   #16
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I have always used (cores+1) as my -j argument, only because that's what I read way back, and have not really re-considered it since.
I have a core2 CPU, so I use -j3; and by the same reasoning, a dual-core CPU with hyperthreading would like to have a -j5

I admit though, the (cores+1) argument has never quite made perfect sense to me: why run a job per CPU, plus an odd job?.. Seems that (cores) would be a better calculation, but really I have never re-evaluated or tested different -j options

I do however use -j1 in cases of code that seems to have race-conditions (or slow dependency resolution?) where parts of the build needed by the next step of the build are not quite available fast enough (cases where make quits because it can't find something, but just typing 'make' again causes the build to resume like nothing went wrong)

Old 07-23-2009, 07:43 AM   #17
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I guess the trick is to use a large enough value of j to keep all your cores busy while some of the tasks are waiting on I/O, without introducing too much task swapping and contention.

I guess the correct value will depend on how good your I/O subsystem is as that will determin what % of the time your cpu's will be sitting idle.

A make modules and bzImage on my crappy old p3-800 takes about 3 hours, but that's also on luks encrypted disks. I normally just 'nice -n 19' it and let it run in the background while I do other stuff.

Looking forward to trying it on my new box, which I'll be installing when Slack 13 releases.

Last edited by GazL; 07-23-2009 at 07:45 AM.


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