[PATCH AUTOSEL 6.11 6/7] setlocalversion: work around "git describe" performance

Sasha Levin
2024-12-04T23:35:31Z

From: Rasmus Villemoes <linux@rasmusvillemoes.dk>

[ Upstream commit 523f3dbc187a9618d4fd80c2b438e4d490705dcd ]

Contrary to expectations, passing a single candidate tag to "git
describe" is slower than not passing any --match options.

$ time git describe --debug
...
traversed 10619 commits
...
v6.12-rc5-63-g0fc810ae3ae1

real 0m0.169s

$ time git describe --match=v6.12-rc5 --debug
...
traversed 1310024 commits
v6.12-rc5-63-g0fc810ae3ae1

real 0m1.281s

In fact, the --debug output shows that git traverses all or most of
history. For some repositories and/or git versions, those 1.3s are
actually 10-15 seconds.

This has been acknowledged as a performance bug in git [1], and a fix
is on its way [2]. However, no solution is yet in git.git, and even
when one lands, it will take quite a while before it finds its way to
a release and for $random_kernel_developer to pick that up.

So rewrite the logic to use plumbing commands. For each of the
candidate values of $tag, we ask: (1) is $tag even an annotated
tag? (2) Is it eligible to describe HEAD, i.e. an ancestor of
HEAD? (3) If so, how many commits are in $tag..HEAD?

I have tested that this produces the same output as the current script
for ~700 random commits between v6.9..v6.10. For those 700 commits,
and in my git repo, the 'make -s kernelrelease' command is on average
~4 times faster with this patch applied (geometric mean of ratios).

For the commit mentioned in Josh's original report [3], the
time-consuming part of setlocalversion goes from

$ time git describe --match=v6.12-rc5 c1e939a21eb1
v6.12-rc5-44-gc1e939a21eb1

real 0m1.210s

to

$ time git rev-list --count --left-right v6.12-rc5..c1e939a21eb1
0 44

real 0m0.037s

[1] https://lore.kernel.org/git/20241101113910.GA2301440@coredump.intra.peff.net/
[2] https://lore.kernel.org/git/20241106192236.GC880133@coredump.intra.peff.net/
[3] https://lore.kernel.org/lkml/309549cafdcfe50c4fceac3263220cc3d8b109b2.1730337435.git.jpoimboe@kernel.org/

Reported-by: Sean Christopherson <seanjc@google.com>
Closes: https://lore.kernel.org/lkml/ZPtlxmdIJXOe0sEy@google.com/
Reported-by: Josh Poimboeuf <jpoimboe@kernel.org>
Closes: https://lore.kernel.org/lkml/309549cafdcfe50c4fceac3263220cc3d8b109b2.1730337435.git.jpoimboe@kernel.org/
Tested-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
scripts/setlocalversion | 54 +++++++++++++++++++++++++++++------------
1 file changed, 38 insertions(+), 16 deletions(-)

diff --git a/scripts/setlocalversion b/scripts/setlocalversion
index 38b96c6797f40..5818465abba98 100755
--- a/scripts/setlocalversion
+++ b/scripts/setlocalversion
@@ -30,6 +30,27 @@ if test $# -gt 0 -o ! -d "$srctree"; then
usage
fi

+try_tag() {
+ tag="$1"
+
+ # Is $tag an annotated tag?
+ [ "$(git cat-file -t "$tag" 2> /dev/null)" = tag ] || return 1
+
+ # Is it an ancestor of HEAD, and if so, how many commits are in $tag..HEAD?
+ # shellcheck disable=SC2046 # word splitting is the point here
+ set -- $(git rev-list --count --left-right "$tag"...HEAD 2> /dev/null)
+
+ # $1 is 0 if and only if $tag is an ancestor of HEAD. Use
+ # string comparison, because $1 is empty if the 'git rev-list'
+ # command somehow failed.
+ [ "$1" = 0 ] || return 1
+
+ # $2 is the number of commits in the range $tag..HEAD, possibly 0.
+ count="$2"
+
+ return 0
+}
+
scm_version()
{
local short=false
@@ -61,33 +82,33 @@ scm_version()
# stable kernel: 6.1.7 -> v6.1.7
version_tag=v$(echo "${KERNELVERSION}" | sed -E 's/^([0-9]+\.[0-9]+)\.0(.*)$/\1\2/')

+ # try_tag initializes count if the tag is usable.
+ count=
+
# If a localversion* file exists, and the corresponding
# annotated tag exists and is an ancestor of HEAD, use
# it. This is the case in linux-next.
- tag=${file_localversion#-}
- desc=
- if [ -n "${tag}" ]; then
- desc=$(git describe --match=$tag 2>/dev/null)
+ if [ -n "${file_localversion#-}" ] ; then
+ try_tag "${file_localversion#-}"
fi

# Otherwise, if a localversion* file exists, and the tag
# obtained by appending it to the tag derived from
# KERNELVERSION exists and is an ancestor of HEAD, use
# it. This is e.g. the case in linux-rt.
- if [ -z "${desc}" ] && [ -n "${file_localversion}" ]; then
- tag="${version_tag}${file_localversion}"
- desc=$(git describe --match=$tag 2>/dev/null)
+ if [ -z "${count}" ] && [ -n "${file_localversion}" ]; then
+ try_tag "${version_tag}${file_localversion}"
fi

# Otherwise, default to the annotated tag derived from KERNELVERSION.
- if [ -z "${desc}" ]; then
- tag="${version_tag}"
- desc=$(git describe --match=$tag 2>/dev/null)
+ if [ -z "${count}" ]; then
+ try_tag "${version_tag}"
fi

- # If we are at the tagged commit, we ignore it because the version is
- # well-defined.
- if [ "${tag}" != "${desc}" ]; then
+ # If we are at the tagged commit, we ignore it because the
+ # version is well-defined. If none of the attempted tags exist
+ # or were usable, $count is still empty.
+ if [ -z "${count}" ] || [ "${count}" -gt 0 ]; then

# If only the short version is requested, don't bother
# running further git commands
@@ -95,14 +116,15 @@ scm_version()
echo "+"
return
fi
+
# If we are past the tagged commit, we pretty print it.
# (like 6.1.0-14595-g292a089d78d3)
- if [ -n "${desc}" ]; then
- echo "${desc}" | awk -F- '{printf("-%05d", $(NF-1))}'
+ if [ -n "${count}" ]; then
+ printf "%s%05d" "-" "${count}"
fi

# Add -g and exactly 12 hex chars.
- printf '%s%s' -g "$(echo $head | cut -c1-12)"
+ printf '%s%.12s' -g "$head"
fi

if ${no_dirty}; then
--
2.43.0