Messages in this thread | | | From | Linus Torvalds <> | Date | Mon, 17 Oct 2016 09:46:09 -0700 | Subject | Re: [4.9-rc1] Build-time 2x slower |
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On Mon, Oct 17, 2016 at 9:04 AM, Sedat Dilek <sedat.dilek@gmail.com> wrote: > > not sure whom to address on this issue. > > I have built Linux v4.9-rc1, v4.8.2 and v4.4.25 kernels (in this > order) this morning. > > Building a Linux v4.8.2 under Linux v4.9-rc1 took two times longer. > > As usually I build with 2 parallel-make-jobs. > This takes approx. 30mins. > Under Linux v4.9-rc1 it took approx. an hour.
Hmm. Would you mind just bisecting it? I've not noticed the same thing on my setup, but to be honest I generally don't time things very closely because the variation for me tends to be much more along the lines of "damn, that pull request touched <linux./fs.h> now it's rebuilding everything" vs "40 seconds to build just the driver that changed". Most of my builds are the "allmodconfig" builds I do in between pulls..
You can even automate it, since it's going to take some time, using "git bisect run" and writing a small script that looks at how long it takes to build the kernel from scratch each time. I'd suggest trying to write the script using a smaller repository (maybe git itself). The script would just needs to do a clean rebuild, time it, and have return success or error based on how long it took.
The script *might* look something like
#!/bin/sh git clean -dqfx make oldconfig time -o time-file -f '%e' sh -c "make -j8 > ../output" # remove fractional seconds time=$(cat time-file | sed 's/\..*//') # less than 35 minutes is good? [ $time -lt $((35*60)) ]
but I didn't really test that very much. Anyway, you *should* be able to do something like
git bisect good v4.8 git bisect bad v4.9-rc1 git bisect run ../timing-script
(put the "timing-script" somewhere _else_ than the kernel sources so that the "git clean" doesn't remove it - that's what my first silly test did ;)
You may have to tweak that script a bit, but I think you get the idea..
Linus
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