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authorShawn O. Pearce <spearce@spearce.org>2006-12-14 11:15:57 (GMT)
committerJunio C Hamano <junkio@cox.net>2006-12-16 06:11:19 (GMT)
commit1510fea781cb0517eeba8c378964f7bc4f9577ab (patch)
tree80be67e623e96f28290834a443c5dd685952115d /Makefile
parent1576f5f7b2addd648a41fb5cfbcd2e6d632b7461 (diff)
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Avoid accessing a slow working copy during diffcore operations.
The Cygwin folks have done a fine job at creating a POSIX layer on Windows That Just Works(tm). However it comes with a penalty; accessing files in the working tree by way of stat/open/mmap can be slower for diffcore than inflating the data from a blob which is stored in a packfile. This performance problem is especially an issue in merge-recursive when dealing with nearly 7000 added files, as we are loading each file's content from the working directory to perform rename detection. I have literally seen (and sadly watched) paint dry in less time than it takes for merge-recursive to finish such a merge. On the other hand this very same merge runs very fast on Solaris. If Git is compiled with NO_FAST_WORKING_DIRECTORY set then we will avoid looking at the working directory when the blob in question is available within a packfile and the caller doesn't need the data unpacked into a temporary file. We don't use loose objects as they have the same open/mmap/close costs as the working directory file access, but have the additional CPU overhead of needing to inflate the content before use. So it is still faster to use the working tree file over the loose object. If the caller needs the file data unpacked into a temporary file its likely because they are going to call an external diff program, passing the file as a parameter. In this case reusing the working tree file will be faster as we don't need to inflate the data and write it out to a temporary file. The NO_FAST_WORKING_DIRECTORY feature is enabled by default on Cygwin, as that is the platform which currently appears to benefit the most from this option. Signed-off-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <junkio@cox.net>
Diffstat (limited to 'Makefile')
-rw-r--r--Makefile7
1 files changed, 7 insertions, 0 deletions
diff --git a/Makefile b/Makefile
index 2d17fa7..676d426 100644
--- a/Makefile
+++ b/Makefile
@@ -69,6 +69,9 @@ all:
#
# Define NO_MMAP if you want to avoid mmap.
#
+# Define NO_FAST_WORKING_DIRECTORY if accessing objects in pack files is
+# generally faster on your platform than accessing the working directory.
+#
# Define NO_IPV6 if you lack IPv6 support and getaddrinfo().
#
# Define NO_SOCKADDR_STORAGE if your platform does not have struct
@@ -355,6 +358,7 @@ ifeq ($(uname_O),Cygwin)
NO_SYMLINK_HEAD = YesPlease
NEEDS_LIBICONV = YesPlease
NO_C99_FORMAT = YesPlease
+ NO_FAST_WORKING_DIRECTORY = UnfortunatelyYes
# There are conflicting reports about this.
# On some boxes NO_MMAP is needed, and not so elsewhere.
# Try uncommenting this if you see things break -- YMMV.
@@ -506,6 +510,9 @@ ifdef NO_MMAP
COMPAT_CFLAGS += -DNO_MMAP
COMPAT_OBJS += compat/mmap.o
endif
+ifdef NO_FAST_WORKING_DIRECTORY
+ BASIC_CFLAGS += -DNO_FAST_WORKING_DIRECTORY
+endif
ifdef NO_IPV6
BASIC_CFLAGS += -DNO_IPV6
endif