Remove unnecessary rpaths in the git-annex binary, but only when it's built using make, not cabal. This speeds up git-annex statup time by around 50%.

CHANGELOG

@@ -6,6 +6,9 @@ git-annex (6.20160614) UNRELEASED; urgency=medium
   * get, drop: Add --batch and --json options.
   * New url for git-remote-gcrypt, now maintained by spwhitton.
   * testremote: Fix crash when testing a freshly made external special remote.
+  * Remove unnecessary rpaths in the git-annex binary, but only when
+    it's built using make, not cabal. 
+    This speeds up git-annex statup time by around 50%.
 
  -- Joey Hess <id@joeyh.name>  Mon, 13 Jun 2016 21:52:24 -0400
 

Makefile

@@ -29,6 +29,8 @@ git-annex: Build/SysConfig.hs
 	else \
 		ln -sf dist/build/git-annex/git-annex git-annex; \
 	fi
+	# Work around https://github.com/haskell/cabal/issues/3524
+	@chrpath -d git-annex || echo "** unable to chrpath git-annex; it will be a little bit slower than necessary"
 
 # These are not built normally.
 git-union-merge.1: doc/git-union-merge.mdwn

debian/control

@@ -85,6 +85,7 @@ Build-Depends:
 	curl,
 	openssh-client,
 	git-remote-gcrypt (>= 0.20130908-6),
+	chrpath,
 Maintainer: Richard Hartmann <richih@debian.org>
 Standards-Version: 3.9.8
 Vcs-Git: git://git.kitenet.net/git-annex

debian/git-annex.lintian-overrides

@@ -1 +0,0 @@
-binary-or-shlib-defines-rpath

doc/todo/could_standalone___39__fixed__39___git-annex_binaries_be_prelinked__63__.mdwn

@@ -3,3 +3,5 @@ Since in datalad we are invoking git and git-annex quite frequently, and on debi
 just an idea
 
 [[!meta author=yoh]]
+
+> [[fixed|done]], but without prelinking. --[[Joey]]

doc/todo/could_standalone___39__fixed__39___git-annex_binaries_be_prelinked__63__/comment_1_1bdc41c22f472d1d6adac563952fe354._comment

@@ -0,0 +1,59 @@
+[[!comment format=mdwn
+ username="joey"
+ subject="""comment 1"""
+ date="2016-07-06T15:59:34Z"
+ content="""
+Startup time is also particulary important when git-annex is being used as
+a smudge/clean filter in v6 mode, since it's run once per file git operates
+on.
+
+---
+
+What I'd look at before prelinking is, does your git-annex executable
+dynamically link haskell libraries?
+
+That was the case for a while in the standalone builds, until I noticed it
+caused too much linker time and put it back to static linking of the
+haskell libs. Leaving only 34 or so C shared libs.
+
+---
+
+Did some preliminary benchmarking here of `git-annex version --raw`
+
+* deb package build: 0.04 seconds min
+* deb package build prelinked: ~0.03 seconds min
+* standalone build: 0.05 seconds min
+* git-annex modified to print "hi" and exit immediately: 0.02 seconds min
+
+So, the overhead of the wrapper scripts for the standalone build is around
+0.01 seconds.
+
+And, prelinking does help a little bit (although probably closer to 0.005
+seconds than 0.01; my measurements are too coarse to get a good number).
+
+Meanwhile, 0.02 seconds are used after git-annex starts up. This overhead
+includes finding the path to the git repository, running and parsing `git
+config --list`, etc.
+
+But what about that 0.02 seconds just to print "hi"...?
+
+----
+
+With strace I noticed a very interesting thing. Despite being statically
+linked against the haskell libraries, the linker searches in all their
+paths for all C libraries. This adds around 30000 failed open() calls
+to git-annex's startup. This is done even after prelinking. It must be a
+significant part of the startup time.
+
+Filed a bug: <https://github.com/haskell/cabal/issues/3524>
+
+Put in a chrpath workaround, but only when git-annex is built with "make"
+(not cabal install git-annex).
+
+Updated benchmarks:
+
+* deb package build: 0.02 seconds min
+* deb package build prelinked: ~0.02 seconds min
+* standalone build: 0.03 seconds min
+* git-annex modified to print "hi" and exit immediately: 0.01 seconds min
+"""]]