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authorThomas Rast <trast@student.ethz.ch>2012-04-06 23:01:23 +0200
committerJunio C Hamano <gitster@pobox.com>2012-04-09 17:03:25 -0700
commit6942efcfa9f3083e7c7863348fa5bb1350412595 (patch)
tree569985c285ef0acea5617a93ebdea46a299f46ee /Makefile
parente8dde3e5f9ddb7cf95a6ff3cea6cf07c3a2db80d (diff)
downloadgit-6942efcfa9f3083e7c7863348fa5bb1350412595.tar.gz
git-6942efcfa9f3083e7c7863348fa5bb1350412595.tar.xz
xdiff: load full words in the inner loop of xdl_hash_record
Redo the hashing loop in xdl_hash_record in a way that loads an entire 'long' at a time, using masking tricks to see when and where we found the terminating '\n'. I stole inspiration and code from the posts by Linus Torvalds around https://lkml.org/lkml/2012/3/2/452 https://lkml.org/lkml/2012/3/5/6 His method reads the buffers in sizeof(long) increments, and may thus overrun it by at most sizeof(long)-1 bytes before it sees the final newline (or hits the buffer length check). I considered padding out all buffers by a suitable amount to "catch" the overrun, but * this does not work for mmap()'d buffers: if you map 4096+8 bytes from a 4096 byte file, accessing the last 8 bytes results in a SIGBUS on my machine; and * it would also be extremely ugly because it intrudes deep into the unpacking machinery. So I adapted it to not read beyond the buffer at all. Instead, it reads the final partial word byte-by-byte and strings it together. Then it can use the same logic as before to finish the hashing. So far we enable this only on x86_64, where it provides nice speedup for diff-related work: Test origin/next tr/xdiff-fast-hash ----------------------------------------------------------------------------- 4000.1: log -3000 (baseline) 0.07(0.05+0.02) 0.08(0.06+0.02) +14.3% 4000.2: log --raw -3000 (tree-only) 0.37(0.33+0.04) 0.37(0.32+0.04) +0.0% 4000.3: log -p -3000 (Myers) 1.75(1.65+0.09) 1.60(1.49+0.10) -8.6% 4000.4: log -p -3000 --histogram 1.73(1.62+0.09) 1.58(1.49+0.08) -8.7% 4000.5: log -p -3000 --patience 2.11(2.00+0.10) 1.94(1.80+0.11) -8.1% Perhaps other platforms could also benefit. However it does NOT work on big-endian systems! [jc: minimum style and compilation fixes] Signed-off-by: Thomas Rast <trast@student.ethz.ch> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Diffstat (limited to 'Makefile')
-rw-r--r--Makefile12
1 files changed, 12 insertions, 0 deletions
diff --git a/Makefile b/Makefile
index be1957a5e..13ed1b1d2 100644
--- a/Makefile
+++ b/Makefile
@@ -288,6 +288,11 @@ all::
# dependency rules.
#
# Define NATIVE_CRLF if your platform uses CRLF for line endings.
+#
+# Define XDL_FAST_HASH to use an alternative line-hashing method in
+# the diff algorithm. It gives a nice speedup if your processor has
+# fast unaligned word loads. Does NOT work on big-endian systems!
+# Enabled by default on x86_64.
GIT-VERSION-FILE: FORCE
@$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -864,6 +869,9 @@ EXTLIBS =
# because maintaining the nesting to match is a pain. If
# we had "elif" things would have been much nicer...
+ifeq ($(uname_M),x86_64)
+ XDL_FAST_HASH = YesPlease
+endif
ifeq ($(uname_S),OSF1)
# Need this for u_short definitions et al
BASIC_CFLAGS += -D_OSF_SOURCE
@@ -1737,6 +1745,10 @@ ifndef NO_MSGFMT_EXTENDED_OPTIONS
MSGFMT += --check --statistics
endif
+ifneq (,$(XDL_FAST_HASH))
+ BASIC_CFLAGS += -DXDL_FAST_HASH
+endif
+
ifeq ($(TCLTK_PATH),)
NO_TCLTK=NoThanks
endif