linux-kernel - Re: About git-bisect (was: Linux 2.6.28-rc7)

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Date:	Tue, 02 Dec 2008 22:52:49 +0100
From:	Francis Moreau <francis.moro@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Sam Ravnborg <sam@...nborg.org>,
	"Renato S. Yamane" <yamane@...mondcut.com.br>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: About git-bisect (was: Linux 2.6.28-rc7)

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> That said, the _best_ way to speed up your compile (whether bisecting or 
> not) is to simply only compile the drivers and modules you actually need. 

That's interesting because I recently tried to strip down my kernel
configuration but I met a problem: I usually don't know if I really
need a feature or not, and that's specially true when configuring the
network stuffs, since I'm not a network expert...

So I still have 254 modules and after recompiling my kernel, I did:

	$ touch kernel/sched.c
	$ time make -j4
	[...]
	MODPOST 254 modules
	[...]
	Kernel: arch/x86/boot/bzImage is ready  (#109)
	
	real    3m23.866s
	user    0m35.006s
	sys     0m15.698s

and here is the time I get if I recompile the kernel without touching
any files:

	$ time make -j4
	  CHK     include/linux/version.h
	  CHK     include/linux/utsrelease.h
	  SYMLINK include/asm -> include/asm-x86
	  CALL    scripts/checksyscalls.sh
	  CHK     include/linux/compile.h
	dnsdomainname: Unknown host
	  CHK     include/linux/version.h
	make[2]: `scripts/unifdef' is up to date.
	  Building modules, stage 2.
	Kernel: arch/x86/boot/bzImage is ready  (#109)
	  MODPOST 254 modules
	
	real      0m53.612s
	user      0m17.996s
	sys       0m9.752s

With these figures, I can confirm that doing bisection, even with 5
reboots, is painful.

> It takes me 16 seconds to compile my kernel (if it's all cached), and 
> that's largely because I do _not_ compile one of the crazy distro kernels 
> with thousands of totally irrelevant modules for my setup.

an other reason is perhaps you're using a computer that most common
mortal don't have ;)

Care to share your network configuration ;) ?

thanks

Francis
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