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Subject[PATCH 033/161] tools/perf/build: Speed up git-version test on re-make
From: Ingo Molnar <>

util/PERF-VERSION-GEN is currently executed on every build attempt,
and this script can take a lot of time on trees that are at a
significant git-distance from Linus's tree:

$ time util/PERF-VERSION-GEN

real 0m4.343s
user 0m4.176s
sys 0m0.140s

It also takes a lot of time if the Git repository is network attached, etc.,
because the commands it uses:

TAG=$(git describe --abbrev=0 --match "v[0-9].[0-9]*" 2>/dev/null )

has to count commits from the nearest tag and thus has to access (and
decompress) every git commit blob on the relevant version path.

Even on Linus's tree it takes 0.28 seconds on a fast box to count all the
commits and get the git version string:

$ time util/PERF-VERSION-GEN

real 0m0.279s
user 0m0.247s
sys 0m0.025s

But the version string only has to be regenerated if the git repository's
head commit changes. So add a dependency of ../../.git/HEAD and touch
the file every time it's regenerated, so that Make's build rules can
pick it up and cache the result:

make: `PERF-VERSION-FILE' is up to date.

real 0m0.184s
user 0m0.117s
sys 0m0.026s

Cc: Arnaldo Carvalho de Melo <>
Cc: Peter Zijlstra <>
Cc: Namhyung Kim <>
Cc: David Ahern <>
Cc: Jiri Olsa <>
Signed-off-by: Ingo Molnar <>
tools/perf/Makefile | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/tools/perf/Makefile b/tools/perf/Makefile
index 64c043b7a438..6b5452a120af 100644
--- a/tools/perf/Makefile
+++ b/tools/perf/Makefile
@@ -70,8 +70,9 @@ ifneq ($(OUTPUT),)
#$(info Determined 'OUTPUT' to be $(OUTPUT))


@@ -814,6 +815,16 @@ clean: $(LIBTRACEEVENT)-clean $(LIBLK)-clean
$(RM) $(OUTPUT)util/*-flex*

+# Trick: if ../../.git does not exist - we are building out of tree for example,
+# then force version regeneration:
+ifeq ($(wildcard ../../.git/HEAD),)
+ GIT-HEAD-PHONY = ../../.git/HEAD
.PHONY: all install clean strip $(LIBTRACEEVENT) $(LIBLK)
.PHONY: shell_compatibility_test please_set_SHELL_PATH_to_a_more_modern_shell

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