Re: Tricks to speed up kernel builds

[Thomas Fjellstrom]

On Tue September 15 2009, Ozan ÃaÄlayan wrote:
> Hi,
> 
> I'd googled a lot about the $subject but couldn't find any detailed
> guide about it. So, the followings are what I understand from what I've
> found:
> 
> 1. Build inside a tmpfs to avoid I/O bottlenecks,
> 2. Use ccache,
> 3. Switch governor to performance if supported,
> 4. Pass -j to gnu make to parallelize the build process,
> 5. Don't build debug symbols a.k.a set CONFIG_DEBUG_INFO=n
> 6. There are a bunch of sched patches in tip which apparently improves
> things during kbuild
> 7. Distribute the work into the local network using icecream, distcc.
> 
> For the -j part, how many jobs should we pass to it? I've seen people
> passing
> 
> - NR_of_cores+1
> - NR_of_cores x 2 (I think that this is useful when there's 2 threads of
> execution per core like HyperThreading?)
> - 64, 128, etc. regardless of the number of cores (Is it really useful
> regardless of the CPU)
> 
> The curious question is *what build times can you get* with your typical
> systems using your speedup tricks (quad core, dual core, etc.) ? What
> are other tricks that I can use to even more speed up the build?
> 
> Do you really use icecream/distcc on your daily test builds?
> 
> How about nicing/ionicing make on an idle system? Will it make any
> difference?

I've only done a few compiles recently, and I only really use icecream and 
make -jX to speed up compile times.

I have a 4 node icecc cluster, three quad cores (one limited to 2 cores), and 
one dual core (limited to a single core), which gives 11 total cores I can 
distribute to, and I usually pass: make -j12

Any higher and I don't really see any speedups, any lower, same difference.

My last kernel compile (2.6.31-git4) took about 9 minutes.

> Thanks a lot
> Ozan Caglayan
> 
> 
> 
> 
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Thomas Fjellstrom
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