Re: 2.6.18-rc1 make -j4 does not run parallel
From: Sam Ravnborg
Date: Sun Aug 13 2006 - 04:07:01 EST
On Sun, Aug 13, 2006 at 12:58:51PM +1000, Keith Owens wrote:
> Dual cpu system.
> 'echo $$' reports current id is 4972
> export KBUILD_OUTPUT=../obj
> make -j4
> Building a 126.96.36.199 tree, 'LANG= pstree -pl 4972' shows multiple tasks
> running in parallel. Even here it is only running 2 instead of the 4
> that I expect.
> | `-cc1(8573)
> build a 2.6.18-rc1 or later tree, make -j4 does not run parallel. All
> pstree output shows a single branch, like this.
> Using 'make -j' without a number or 'make -j<n>' where <n> is greater
> than 4 does show parallel build behaviour. Looks like something is
> decrementing -j<n> as you go down the make tree and decrementing it
> enough that it ends up in a serial build.
Thanks. I will try to look into this within a few days - it looks
strange. But you pstree is a great way to see when it happens.
I have been tossing around with an idea to do some of the veru initial
steps in a shell script rather than in make. This should allow us to
bring down the make invocations but this bug needs to be understood
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