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

[Hans Beckérus]

On Sat, Nov 9, 2013 at 11:58 PM, Richard Purdie
<richard.purdie at linuxfoundation.org> wrote:
> On Sat, 2013-11-09 at 21:38 +0100, Andrea Adami wrote:
>> On Fri, Nov 8, 2013 at 6:23 PM, Hart, Darren <darren.hart at intel.com> wrote:
>> > 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
>> >
>> > _______________________________________________
>> > Openembedded-core mailing list
>> > Openembedded-core at lists.openembedded.org
>> > http://lists.openembedded.org/mailman/listinfo/openembedded-core
>>
>> On my old quad core:
>>
>> Before: 95.24 seconds
>> After: 83.25 seconds
>
> We have some "standard" tests we use for comparison purposes as detailed
> on:
>
> https://wiki.yoctoproject.org/wiki/Performance_Test
>
> Some numbers from master and a test branch containing the recent
> speedups:
>
> fedora19,master:d6cc7c8ed76c8b1117cf03c7bd4b0742f98f79b3,poky-10.0.0.final-359-gd6cc7c8,1:22:37,12:05.50,1:17:53,4:02.68,0:31.71,0:15.70,0:01.61,26347744,5035816
> fedora19,master:d6cc7c8ed76c8b1117cf03c7bd4b0742f98f79b3,poky-10.0.0.final-359-gd6cc7c8,1:22:59,12:09.26,1:17:29,4:06.75,0:31.82,0:15.69,0:01.70,26348556,5035876
> fedora19,master:d6cc7c8ed76c8b1117cf03c7bd4b0742f98f79b3,poky-10.0.0.final-359-gd6cc7c8,1:22:21,12:07.23,1:18:21,4:07.44,0:31.79,0:15.63,0:01.62,26351088,5035908
> fedora19,master:d6cc7c8ed76c8b1117cf03c7bd4b0742f98f79b3,poky-10.0.0.final-359-gd6cc7c8,1:23:16,12:15.33,1:18:00,4:02.50,0:31.87,0:15.74,0:01.63,26348132,5035848
> fedora19,rpurdie/timing:9d8c0ef3349936b3bd0bbf485b50cf81f4feaf80,poky-10.0.0.final-373-g9d8c0ef,1:19:42,10:28.53,1:15:30,4:12.24,0:31.30,0:15.69,0:01.66,26137344,5055628
> fedora19,rpurdie/timing2:eb2221d6247c12322ac38b9ac6f24c9de5877e53,poky-10.0.0.final-401-geb2221d,1:18:51,10:44.26,1:16:32,4:13.47,0:31.27,0:15.69,0:01.65,26137828,5055916
>
> So we have 1:23m -> 1:19m for overall buildtime and 12.0m -> 10.5m for
> "bitbake virtual/kernel" from cleansstate. Not too bad :)
>
> Thanks to Stefan for running the tests!
>

I am having some trouble with these patches :( The new approach is
using the '-n' flag to the 'cp' command.
That is not supported on our SuSE11 based system. To be honest, I do
not know how portable '-n' is?
Some system have it, others seems to provide '-u' instead. I guess by
removing '-n' part of the performance gain is lost?
Would it be possible to test for error from the 'cp' command and if it
fails try '-u' instead (and cache the result)? Or maybe
even better, make this configurable in local.conf (or the distro) for
the build platforms that does not support  '-n' but can
instead fall-back to using '-u'. From what I can tell most systems
support  one or the other, but never both.

Thanks.
Hans


> Cheers,
>
> Richard
>
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