Re: [PATCH v1 1/4] fastindex: speed up index load through parallelization

[Jeff King <peff@peff.net>]

On Mon, Nov 20, 2017 at 09:20:35AM -0500, Jeff King wrote:

> Out of curiosity, have you tried experimenting with any high-performance
> 3rd-party allocator libraries? I've often wondered if we could get a
> performance improvement from dropping in a new allocator, but was never
> able to measure any real benefit over glibc's ptmalloc2. The situation
> might be different on Windows, though (i.e., if the libc allocator isn't
> that great).

Just linking with tcmalloc, like:

diff --git a/Makefile b/Makefile
index ee9d5eb11e..4f299cd914 100644
--- a/Makefile
+++ b/Makefile
@@ -1018,7 +1018,7 @@ BUILTIN_OBJS += builtin/worktree.o
 BUILTIN_OBJS += builtin/write-tree.o
 
 GITLIBS = common-main.o $(LIB_FILE) $(XDIFF_LIB)
-EXTLIBS =
+EXTLIBS = -ltcmalloc
 
 GIT_USER_AGENT = git/$(GIT_VERSION)
 

seems to consistently show about 30% speedup on p0002:

Test                                          HEAD^             HEAD                  
--------------------------------------------------------------------------------------
0002.1: read_cache/discard_cache 1000 times   0.19(0.18+0.01)   0.13(0.12+0.01) -31.6%

I don't think we really even need a patch for it. You should be able to
just build with:

  make EXT_LIBS=-ltcmalloc

I can't think of any real advantage to a Makefile knob except
discoverability.

-Peff