On Wed, Jan 31, 2024 at 10:48:47AM +0000, John Garry wrote:

When hacking it is a waste of time and compute energy that we need to
rebuild much kernel code just for changing the head git commit, like this:

quoted

touch include/generated/utsrelease.h 
time make  -j3

mkdir -p /home/john/mnt_sda4/john/kernel-dev2/tools/objtool && make O=/home/john/mnt_sda4/john/kernel-dev2 subdir=tools/objtool --no-print-directory -C objtool 
  INSTALL libsubcmd_headers
  CALL    scripts/checksyscalls.sh
  CC      init/version.o
  AR      init/built-in.a
  CC      kernel/sys.o
  CC      kernel/module/main.o
  AR      kernel/module/built-in.a
  CC      drivers/base/firmware_loader/main.o
  CC      kernel/trace/trace.o
  AR      drivers/base/firmware_loader/built-in.a
  AR      drivers/base/built-in.a
  CC      net/ethtool/ioctl.o
  AR      kernel/trace/built-in.a
  AR      kernel/built-in.a
  AR      net/ethtool/built-in.a
  AR      net/built-in.a
  AR      drivers/built-in.a
  AR      built-in.a
  ...

Files like drivers/base/firmware_loader/main.c needs to be recompiled as
it includes generated/utsrelease.h for UTS_RELEASE macro, and utsrelease.h
is regenerated when the head commit changes.

Introduce global char uts_release[] in init/version.c, which this
mentioned code can use instead of UTS_RELEASE, meaning that we don't need
to rebuild for changing the head commit - only init/version.c needs to be
rebuilt. Whether all the references to UTS_RELEASE in the codebase are
proper is a different matter.

For an x86_64 defconfig build for this series on my old laptop, here is
before and after rebuild time:

before:
real    0m53.591s
user    1m1.842s
sys     0m9.161s

after:
real    0m37.481s
user    0m46.461s
sys     0m7.199s

Sending as an RFC as I need to test more of the conversions and I would
like to also convert more UTS_RELEASE users to prove this is proper
approach.

I like it, I also think that v4l2 includes this as well as all of those
drivers seem to rebuild when this changes, does that not happen for you
too?

Anyway, if the firmware changes work, I'm all for this, thanks for
taking it on!

thanks,

greg k-h