There is no limitation like that, but it's quite easy to break that, you mentioned some ugly BSP before, I wouldn't be surprised if it's broken there.

What worked well for me over the years is using this script:
openembedded-core/scripts/sstate-diff-machines.sh
on jenkins which produces the sstate-cache, it not only checks for signature issues between MACHINEs (can be used for single MACHINE as well) but creates a directory with all sstate signatures in our builds, this is then published as tarball together with built images.

Then when I'm seeing unexpected low reuse of sstate on some builder, I just use the same sstate-diff-machines.sh locally, fetch the tarball from the build I was trying to reproduce and compare the content with bitbake-diffsigs.

Cheers,

On Wed, May 27, 2020 at 10:59 AM Mans Zigher <mans.zigher@...> wrote:

Hi,

This is maybe more related to bitbake but I start by posting it here.
I am for the first time trying to make use of a distributed sstate
cache but I am getting some unexpected results and wanted to hear if
my expectations are wrong. Everything works as expected when a build
node is using a sstate cache from it's self so I do a clean build and
upload the sstate cache from that build to our mirror. If then do a
complete build using the mirror I get a 99% hit rate which is what I
would expect. If I then start a build on a different node using the
same cache I am only getting a 16% hit rate. I am running the builds
inside docker so the environment should be identical. We have several
build nodes in our CI and they where actually cloned and all of them
have the same HW. They are all running the builds in docker but it
looks like they can share the sstate cache and still get a 99% hit
rate. This to me suggests that the hit rate for the sstate cache is
node depending so a cache cannot actually be shared between different
nodes which is not what I expected. I have not been able find any
information about this limitation. Any clarification regarding what to
expect from the sstate cache would be appreciated.

Thanks