How to reduce the time of kernel's re-compiling?
 

Hi, when I compile the kernel of N900(2.6.28-omap1) for the first time in scratchbox, the time is quite long, everyone knows that. And then I made some change of the kernel, recompile it, now the compile time becomes short.

But if I quit scratchbox and re-login it again, and re-compile the kernel, the time is as long as the first time I do it. Does anyone know why? And how to solve this problem?
Thanks!

Re: How to reduce the time of kernel's re-compiling?
 

Get a faster computer?

Re: How to reduce the time of kernel's re-compiling?
 

Maybe some timestamp won't match anymore after logout/login. Use verbose build to se what it's doing.
Maybe even try ccache if that might help recompiles.

Re: How to reduce the time of kernel's re-compiling?
 

Ccache is installed and used by default, that's why the second compilation is much faster. I've no idea why logging out of scratchbox makes it longer for the OP though.

Re: How to reduce the time of kernel's re-compiling?
 

Do you have a bunch of spare cores in your CPU? I tend to increase the number of jobs to run in parallel based on the number of CPU's and cores I have. Eg.

make -j 4 bzImage

This should speed things along a tad assuming you have a quad core machine, though you can vary the number up or down depending.

Re: How to reduce the time of kernel's re-compiling?
 

If it's the same as Gentoo then it's -j total number of cores + 1

Re: How to reduce the time of kernel's re-compiling?
 

Yes, that is a good way and I have done that.

Re: How to reduce the time of kernel's re-compiling?
 

This is a good suggestion, I will try it.

Re: How to reduce the time of kernel's re-compiling?
 

I think your answer is most reasonable. Unfortunately I cannot repeat what I mentioned. Now whenever I recompile the kernel under scratchbox(in any case), the compile time is short. I don't know why.

Re: How to reduce the time of kernel's re-compiling?
 

No, it's just -j <Total Number of Cores> only. Not plus 1 :-) You wont see any improvement unfortunately. +2 or more above the number of cores and you're more likely to have compile times take (sometimes significantly) longer.