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From: John Garry <john.g.garry@oracle.com>
To: mcgrof@kernel.org, russ.weight@linux.dev, gregkh@linuxfoundation.org,
        rafael@kernel.org, rostedt@goodmis.org, mhiramat@kernel.org,
        mathieu.desnoyers@efficios.com, davem@davemloft.net,
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Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org,
        netdev@vger.kernel.org, linux-kbuild@vger.kernel.org,
        John Garry <john.g.garry@oracle.com>
Subject: [PATCH RFC 0/4] Introduce uts_release
Date: Wed, 31 Jan 2024 10:48:47 +0000
Message-Id: <20240131104851.2311358-1-john.g.garry@oracle.com>
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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:

> 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.

John Garry (4):
  init: Add uts_release
  tracing: Use uts_release
  net: ethtool: Use uts_release
  firmware_loader: Use uts_release

 drivers/base/firmware_loader/main.c | 39 +++++++++++++++++++++++------
 include/linux/utsname.h             |  1 +
 init/version.c                      |  3 +++
 kernel/trace/trace.c                |  4 +--
 net/ethtool/ioctl.c                 |  4 +--
 5 files changed, 39 insertions(+), 12 deletions(-)

-- 
2.35.3