When building out-of-tree kernel modules in eSDK, it will always trigger a new rebuilding of kernel, which consumes lots of time. I have tried to add virtual/kernel:do_shared_workdir to sstate cache and ship it with eSDK. On the eSDK side, run `bitbake linux-yocto -c shared_workdir` returns immediatlely, but `bitbake hello-mod` still triggers tasks from linux-yocto:do_fetch. Adding this enhancement, it may need more time to generate the eSDK installer, but it will save considerably time at the eSDK user's side.
As discussed on the mailing list, this is not something we plan to support. There is no technical reason that do_shared_workdir couldn't be an sstate task however the combination of the kernel source and the kernel compiled artifacts is large and results in a large sstate object. This means the time to build the kernel increases substantially. Using the the object in a new build, or in an eSDK then results in having to transfer a large object over a network which is also slow unless its a local transfer so there is a double hit. We made a decision as a project to just rebuild these pieces if/as needed rather than take the hit on the performance of the base kernel builds. I appreciate that doesn't work for every workload but it is the tradeoff we decided to make. If should be possible to patch do_shared_work to be an sstate task, however that code path will be quite different from the current behavior. We don't have the build resources to be able to test these two different code paths (does devtoool work with both, do external modules work with both etc). We're therefore unlikely to merge such a patch. I've cc'd Bruce in case he has any different viewpoint on this.
Just to additionally note, there was a change submitted which makes it easier to implement this: http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=aa83cb5264554dd1963042f905688afc796e98d0 I decided to merge that to at least make this option easier to implement.
Just documenting that my view is the same as RPs. What made it into the tree looks appropriate.
Created attachment 4421 [details] add STAGING_KERNEL_BUILDDIR and STAGING_KERNEL_DIR to eSDK For anyone that may need this acceleration, this patch is for your reference. Apply this patch as well as http://git.yoctoproject.org/cgit.cgi/poky/commit/?id=aa83cb5264554dd1963042f905688afc796e98d0. My testing result: With patch: Orig: =========== ===== build and export eSDK: ---------------------- real 72m28.549s real 69m17.119s user 653m12.390s user 645m38.162s sys 154m17.175s sys 153m22.593s eSDK installer size: -------------------- 4.6G 4.4G eSDK installation: ------------------ real 6m40.714s real 8m7.331s user 24m19.822s user 25m41.045s sys 4m17.492s sys 4m23.538s build hello-mod in eSDK: ------------------------ real 0m31.966s real 21m7.686s user 3m48.485s user 35m10.894s sys 0m7.827s sys 15m3.837s