[yocto] sstate black hole?

[Gary Thomas]

I'm building for multiple ARM i.MX6 platforms.  These have
the same SoC, but slightly different peripherals. As far as
I can tell, they should be able to share everything except
for a few ${MACHINE} specific packages, e.g. the kernel and
u-boot.

Sadly, that doesn't seem to be the case.  The architecture
specific packages are being split into two categories - plain
ARM/Cortex-A9 and those that have i.MX6 specific optimizations.
For example, after building a complete image (on the order of
core-image-sato), I have this split:
$ ls tmp/work/cortexa9hf-vfp-neon-amltd-linux-gnueabi/
acl                  gst-player                 libsamplerate0         modutils-initscripts  shadow-sysroot
alsa-utils           gst-plugins-bad            libsm                  mpeg2dec              shared-mime-info
apmd                 gst-plugins-good           libsndfile1            mplayer2              speex
atk                  gst-plugins-ugly           libsoup-2.4            mtdev                 sqlite3
attr                 gstreamer                  libtheora              ncurses               startup-notification
base-passwd          gstreamer1.0               libtirpc               neon                  strace
    ...
gst-ffmpeg           libpostproc                matchbox-wm            scrnsaverproto        zlib
gst-fluendo-mpegmux  libproxy                   mkfontdir              settings-daemon
gst-meta-base        libpthread-stubs           mkfontscale            shadow

$ ls tmp/work/cortexa9hf-vfp-neon-mx6qdl-amltd-linux-gnueabi/
alsa-lib      gst-plugins-base           imx-gpu-viv  libfslparser   libsdl      xf86-video-imxfb-vivante
cairo         gstreamer1.0-plugins-bad   libdrm       libfslvpuwrap  mesa        xserver-xorg
firmware-imx  gstreamer1.0-plugins-base  libfslcodec  libglu         pulseaudio

It's the second category that is causing problems.  They do not
seem to end up in any shareable sstate at all.  If I try to rebuild
using only sstate, i.e. build my complete image to success, then
remove 'tmp' and rebuild, using the sstate-cache from the first go,
all of the above packages (alsa-lib, ..., xserver-xorg) are all
rebuilt from scratch.  Those recipes do seem to end in my sstate-cache,
but they are never reused from it.

What would make this happen?  How can I prevent it?

As is, sstate is not really shareable between these i.MX6 targets
as so much is being rebuilt all the time...

Any ideas or pointers gladly welcomed.

Thanks

-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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