[yocto] sstate-cache clobbering

[Khem Raj]

On Jul 3, 2013, at 10:06 PM, Trevor Woerner <trevor.woerner at linaro.org> wrote:

> Let's say I have two build machines (A and B), both running the exact
> same version of a given distribution. Also assume both machines have a
> fully populated "downloads" directory but otherwise have not performed
> any OE/Yocto builds.
> 
> On machine A I perform a fresh "bitbake core-image-minimal" and end up
> with a sstate-cache of 733MB and I receive a message saying 324/1621
> tasks didn't need to be (re)run.
> 
> I then take this sstate-cache directory, copy it to machine B and
> perform a "bitbake core-image-minimal". This build takes under 5
> minutes, and didn't need to run 1374/1621 tasks.
> 
> So far this makes good sense. The sstate-cache is getting hit quite a
> lot and the performance of the second build shows considerable
> improvement (relative to the first build on machine A) to reflect this
> fact.
> 
> Now I wipe machine B then get it ready for a fresh build (i.e. put the
> "downloads" directory in place, make sure it has all the necessary
> host packages, etc). Then on machine A I perform a "bitbake
> core-image-minimal -c populate_sdk". Now, on machine A, I end up with
> a sstate-cache that is 1.6GB in size. I take machine A's 1.6GB
> sstate-cache and copy it to machine B. Then on machine B I perform a
> "bitbake core-image-minimal".
> 
> I would have expected this build on machine B to take the same "under
> 5 minutes, and didn't need to run 1374/1621 tasks". But instead I find
> this build takes 27 minutes and only 781/1621 tasks didn't need to be
> run.

hmm you need to compare signatures( bitbake-diffsigs is your friend),
may be there is a variable that should be added
to ignore list which is causing unnecessary rebuilds.

secondly, why are you copying sstate, set up a nfssever/http on machine A
and let it server sstate to machine B via NFS or http


> 
> Doesn't it seem strange that a larger sstate-cache involving the same
> base image has such a lower sstate-cache hit rate?
> _______________________________________________
> yocto mailing list
> yocto at yoctoproject.org
> https://lists.yoctoproject.org/listinfo/yocto