Suggestions request for speed-up kernel compilation

Suggestions request for speed-up kernel compilation

[Alessio Igor Bogani]

Hi All,

Sorry for my bad English.

I'm a kernel newbie and I would be very happy to receive some tips
about kernel compilation from experienced developers.

I have recently elaborated some trivial patches. For each one I have
done a build test at minimum and I find myself spend a lot of time
waiting my Core Duo to accomplish this task. Make is a very smart tool
but after a git pull or a git fetch origin/git reset --hard origin it
can't help as desired.

Unfortunately I don't have a clustered compilation farm under my control. :-)

Anyone can suggest me how mitigate that issue?

Tips, RTFM, links will be appreciated as long as referred to real used
technique.

Thanks in advance and sorry for stupid question.

Ciao,
Alessio

Re: Suggestions request for speed-up kernel compilation

[Sven-Haegar Koch]

On Fri, 24 Apr 2009, Alessio Igor Bogani wrote:

> I'm a kernel newbie and I would be very happy to receive some tips
> about kernel compilation from experienced developers.
> 
> I have recently elaborated some trivial patches. For each one I have
> done a build test at minimum and I find myself spend a lot of time
> waiting my Core Duo to accomplish this task. Make is a very smart tool
> but after a git pull or a git fetch origin/git reset --hard origin it
> can't help as desired.
> 
> Unfortunately I don't have a clustered compilation farm under my control. :-)
> 
> Anyone can suggest me how mitigate that issue?

What helps me with this is using ccache (compiler cache) - it keeps the 
compile results inside a cache and when compiling the same file again it 
fetches the result from there.

on debian it is just:
  apt-get install ccache
  export PATH=/usr/lib/ccache:$PATH
  ...work on kernel like normal...


c'ya
sven

-- 
The lights are fading out, once more...

Re: Suggestions request for speed-up kernel compilation

[Sam Ravnborg]

On Fri, Apr 24, 2009 at 11:57:35AM +0200, Alessio Igor Bogani wrote:
> Hi All,
> 
> Sorry for my bad English.
> 
> I'm a kernel newbie and I would be very happy to receive some tips
> about kernel compilation from experienced developers.
> 
> I have recently elaborated some trivial patches. For each one I have
> done a build test at minimum and I find myself spend a lot of time
> waiting my Core Duo to accomplish this task. Make is a very smart tool
> but after a git pull or a git fetch origin/git reset --hard origin it
> can't help as desired.
> 
> Unfortunately I don't have a clustered compilation farm under my control. :-)
> 
> Anyone can suggest me how mitigate that issue?
The kernel build system does a good job detecting what to build.
So if you touches a .h file or you change a CONFIG_ symbol used by
a header file you will see a lot of rebuilds - sometimes
more than you expected.

Try to do:

    make V=2

to see why a certain file is rebuild.


If you know you only have to build a single file you can use:

    make kernel/foo.o

If you want to build a directory - including sub-directories:

   make kernel/

If you want to build a specific module use:

    make drivers/net/foobar.ko

make help can give you a few more hints.

And try to avoid "make clean" / "make mrproper" - as this deletes all .o files.

	Sam

Re: Suggestions request for speed-up kernel compilation

[Richard Kennedy]

Alessio Igor Bogani wrote:
> Hi All,
> 
> Sorry for my bad English.
> 
> I'm a kernel newbie and I would be very happy to receive some tips
> about kernel compilation from experienced developers.
> 
> I have recently elaborated some trivial patches. For each one I have
> done a build test at minimum and I find myself spend a lot of time
> waiting my Core Duo to accomplish this task. Make is a very smart tool
> but after a git pull or a git fetch origin/git reset --hard origin it
> can't help as desired.
> 
> Unfortunately I don't have a clustered compilation farm under my control. :-)
> 
> Anyone can suggest me how mitigate that issue?
> 
> Tips, RTFM, links will be appreciated as long as referred to real used
> technique.
> 
> Thanks in advance and sorry for stupid question.
> 
> Ciao,
> Alessio

check you're using enough make jobs for your processor & memory.
On my AMDX2 I find 'make -j 8' is quickest for a full rebuild.
regards
Richard

Re: Suggestions request for speed-up kernel compilation

[Al Viro]

On Fri, Apr 24, 2009 at 11:57:35AM +0200, Alessio Igor Bogani wrote:
> Hi All,
> 
> Sorry for my bad English.
> 
> I'm a kernel newbie and I would be very happy to receive some tips
> about kernel compilation from experienced developers.
> 
> I have recently elaborated some trivial patches. For each one I have
> done a build test at minimum and I find myself spend a lot of time
> waiting my Core Duo to accomplish this task. Make is a very smart tool
> but after a git pull or a git fetch origin/git reset --hard origin it
> can't help as desired.

ccache, for normal times, as suggested in other reply.  But if you or
mainline or something you've pulled change the headers, there's not much
to be done, unfortunately...

Re: Suggestions request for speed-up kernel compilation

[Andi Kleen]

Alessio Igor Bogani <abogani@texware.it> writes:

> I'm a kernel newbie and I would be very happy to receive some tips
> about kernel compilation from experienced developers.
>

Some tricks:

If you just want to test that the file you've been hacking
on compiles you can use make dir/path/file.o

Use the minimum config file for your machines, 
except for occasional fuller verification builds

Set the right -j make level. You have to experiment 
what is best.

Not enabling CONFIG_DEBUGINFO speeds up compilation significantly

When you use ccache make sure you have the cache directory on
the same partition and enable CCACHE_HARDLINK=1. Alternatively
what also works (but is a bit more expensive) is to put
the ccache cache on a SSD.

What works very well is to throw some money at it -- compilation
scales very well in a cluster. Get the cheapest quad core you can get
as an additional machine and use a tool like icecream
(http://en.opensuse.org/Icecream) to distribute the compilation.

You need special wrappers like 
ftp://firstfloor.org/pub/ak/smallsrc/icecache.c to combine
icecream with ccache

I also found using the "gold" linker in latest binutils
speeds up builds because especially when you already
have parallel compilations the linker is often a bottleneck.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.