Another build speedup, while at it.
===============>
Subject: perf tools: Speed up git-version test on re-make
From: Ingo Molnar <mi...@kernel.org>
Date: Tue Oct 1 16:28:09 CEST 2013
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
So the version generation overhead is completely gone for re-builds.
Signed-off-by: Ingo Molnar <mi...@kernel.org>
---
tools/perf/Makefile | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)
Index: tip/tools/perf/Makefile
===================================================================
--- tip.orig/tools/perf/Makefile
+++ tip/tools/perf/Makefile
@@ -70,8 +70,9 @@ ifneq ($(OUTPUT),)
#$(info Determined 'OUTPUT' to be $(OUTPUT))
endif
-$(OUTPUT)PERF-VERSION-FILE: .FORCE-PERF-VERSION-FILE
+$(OUTPUT)PERF-VERSION-FILE: ../../.git/HEAD
@$(SHELL_PATH) util/PERF-VERSION-GEN $(OUTPUT)
+ @touch $(OUTPUT)PERF-VERSION-FILE
CC = $(CROSS_COMPILE)gcc
AR = $(CROSS_COMPILE)ar
@@ -813,7 +814,17 @@ clean: $(LIBTRACEEVENT)-clean $(LIBLK)-c
$(RM) $(OUTPUT)util/*-flex*
$(python-clean)
+#
+# Trick: if ../../.git does not exist - we are building out of tree for
example,
+# then force version regeneration:
+#
+ifeq ($(wildcard ../../.git/HEAD),)
+ GIT-HEAD-PHONY = ../../.git/HEAD
+else
+ GIT-HEAD-PHONY =
+endif
+
.PHONY: all install clean strip $(LIBTRACEEVENT) $(LIBLK)
.PHONY: shell_compatibility_test please_set_SHELL_PATH_to_a_more_modern_shell
-.PHONY: .FORCE-PERF-VERSION-FILE TAGS tags cscope .FORCE-PERF-CFLAGS
+.PHONY: $(GIT-HEAD-PHONY) TAGS tags cscope .FORCE-PERF-CFLAGS
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