Last month our friends at Codethink were guests on FLOSS Weekly, talking about Baserock. Baserock is a new embedded build system with some interesting features/quirks (depending on your point of view) that I won’t go into. What caught my attention was the discussion about build times for various embedded build systems.
Yocto, again, if you want to do a clean build it will take days to build your system, even if you do an incremental build, even if you just do a single change and test it, that will take hours.
(source: FLOSS Weekly #230, timestamp 13:21, slightly edited for clarity)
Now “days” for a clean build and “hours” for re-building an image with a single change is quite excessive for the Yocto Project, but also quite specific. I asked Rob Taylor where he was getting these durations from, and he corrected himself on Twitter:
@rossburton Sorry, I didn't think I'd said days. Hours is obviously correct.
— Rob Taylor (@robtaylor78) October 30, 2012
I’m not sure if he meant “hours” for both a full build and an incremental build, or whether by “hours” for incremental he actually meant “minutes”, but I’ll leave this for now and talk about real build times.
Now, my build machine is new but nothing special. It’s built around an Intel Core i7-3770 CPU (quad-core, 3.4GHz) with 16GB of RAM (which is overkill, but more RAM means more disk cache which is always good), and two disks: a 250GB Western Digital Blue for /, and a 1TB Western Digital Green for /data (which is where the builds happen). This was built by PC Specialist for around £600 (the budget was $1000 without taxes) and happily sits in my home study running a nightly build without waking the kids up. People with more money stripe /data across multiple disks, use SSDs, or 10GB tmpfs filesystems, but I had a budget to stick to.
So, let’s wipe my build directory and do another build from scratch (with sources already downloaded). As a reference image I’ll use core-image-sato, which includes an X server, GTK+, the Matchbox window manager suite and some demo applications. For completeness, this is using the 1.3 release – I expect the current master branch to be slightly faster as there’s some optimisations to the housekeeping that have landed.
$ rm -rf /data/poky-master/tmp/
$ time bitbake core-image-sato
Pseudo is not present but is required, building this first before the main build
Parsing of 817 .bb files complete (0 cached, 817 parsed). 1117 targets, 18 skipped, 0 masked, 0 errors.
...
NOTE: Tasks Summary: Attempted 5393 tasks of which 4495 didn't need to be rerun and all succeeded.
real 9m47.289s
Okay, that was a bit too fast. What happened is that I wiped my local build directory, but it’s pulling build components from the “shared state cache”, so it spent six minutes reconstructing a working tree from shared state, and then three minutes building the image itself. The shared state cache is fantastic, especially as you can share it between multiple machines. Anyway, by renaming the sstate directory it won’t be found, and then we can do a proper build from scratch.
$ rm -rf /data/poky-master/tmp/
$ mv /data/poky-master/sstate /data/poky-master/sstate-old
$ time bitbake core-image-sato
Pseudo is not present but is required, building this first before the main build
...
NOTE: Tasks Summary: Attempted 5117 tasks of which 352 didn't need to be rerun and all succeeded.
real 70m37.298s
user 326m45.417s
sys 37m13.304s
That’s a full build from scratch (with downloaded sources, we’re not benchmarking my ADSL) in just over an hour on affordable commodity hardware. As I said this isn’t some “minimal” image that boots straight to busybox, this is building a complete cross-compiling toolchain, the kernel, X.org, GTK+, GStreamer, the Matchbox window manager/panel/desktop, and finally several applications. In total, 431 source packages were built and packaged, numerous QA tests executed and flashable images generated.
My configuration is to build for Intel Atom but a build for an ARM, MIPS, or PowerPC target would also take a similar amount of time, as even what could be considered “native” targets (targeting Atom, building on i7) doesn’t always turn out to be native: for example carrier-grade Xeon’s have instructions that my i7 doesn’t have, and if you were building carrier-grade embedded software you’d want to ensure they were used.
So, next time someone claims Yocto Project/OpenEmbedded takes “days” or even “hours” to do a build, you can denounce that as FUD and point them here!