[OE-core] [PATCH] kernel: Use hardlinks for do_populate_sysroot for speed

[Hart, Darren]

On Fri, 2013-11-08 at 16:50 +0000, Richard Purdie wrote:
> On Fri, 2013-11-08 at 10:59 -0500, Bruce Ashfield wrote:
> > On 13-11-08 10:55 AM, Richard Purdie wrote:
> > > On Fri, 2013-11-08 at 10:41 -0500, Bruce Ashfield wrote:
> > >> On 13-11-08 10:18 AM, Richard Purdie wrote:
> > >>> The kernel tree is large and doesn't need to be copied. Override
> > >>> the default sysroot handling function to use a hardlink copying
> > >>> function in python.
> > >>>
> > >>> This commit also drops the copying of the /lib directory which
> > >>> just contains the kernel modules. We never use those in the sysroot
> > >>> so there is little point in carrying those around.
> > >>>
> > >>> For linux-yocto this takes the do_populate_sysroot time 24s -> 14s.
> > >>
> > >> Fantastic. One less thing for me to dig into later. I thought this
> > >> was already in place, so I'm pleasantly surprised that there was a
> > >> time savings to be found!
> > >
> > > I was somewhat surprised too.
> > >
> > > We still need to optimise what we install in do_install since that is
> > > where significant gains can still be made.
> > 
> > Agreed. I started some changes in that area right after ELC-e, I'll
> > try and get them out sooner rather than later.
> 
> I thought I'd share this for people's interest:
> 
> http://dan.rpsys.net/kernelbuildissue.png
> 
> Its the output from pybootchart of a bitbake core-image-sato from
> scratch. I've zoomed out to put some bars in particular into
> perspective.
> 
> The pink colour is linux-yocto:do_install, the cyan is
> linux-yocto:do_package and the blue is linux-yocto:do_populate_sysroot.
> The uncoloured bar at the bottom is linux-yocto:do_package_write_rpm.
> 
> So the final thing to build is the kernel by quite some margin, its
> holding the rest of the build up.
> 
> Hopefully these patches start to improve that a bit!
> 

Yup, linux-yocto do_package is the biggest build-time hindrance for me
and something we've wanted to look into for a long time. Great to see
some progress.

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel