linux-kernel - Tricks to speed up kernel builds

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Date:	Tue, 15 Sep 2009 11:22:37 +0300
From:	Ozan Çağlayan <ozan@...dus.org.tr>
To:	linux-kernel <linux-kernel@...r.kernel.org>
CC:	mingo@...hat.com
Subject: Tricks to speed up kernel builds

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?

Thanks a lot
Ozan Caglayan

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