Don't apply this patch and change GIT_COMPRESSION unless you know what you are doing and why you are doing it. You will break an older version of git. You may break a newer version of git. You have been warned.
I also note that there's a bzlib out there.
cache.h: 828d660ab82bb35a1ca632a2ba4620dc483889bd --- a/cache.h +++ b/cache.h @@ -16,6 +16,8 @@ #include <openssl/sha.h> #include <zlib.h>
+#define GIT_COMPRESSION Z_BEST_COMPRESSION + /* * Basic data structures for the directory cache * sha1_file.c: 754e8b4e9ea8104df48152f875d6b874304e2a62 --- a/sha1_file.c +++ b/sha1_file.c @@ -199,7 +199,7 @@ int write_sha1_file(char *buf, unsigned
/* Set it up */ memset(&stream, 0, sizeof(stream)); - deflateInit(&stream, Z_BEST_COMPRESSION); + deflateInit(&stream, GIT_COMPRESSION); size = deflateBound(&stream, len); compressed = malloc(size);
update-cache.c: a09883541c745c76413c62109a80f40df4b7a7fb --- a/update-cache.c +++ b/update-cache.c @@ -40,7 +40,7 @@ static int index_fd(unsigned char *sha1, SHA1_Final(sha1, &c);
memset(&stream, 0, sizeof(stream)); - deflateInit(&stream, Z_BEST_COMPRESSION); + deflateInit(&stream, GIT_COMPRESSION);
/* * ASCII size + nul byte
Mike Taht wrote:
Just to clarify this was a git add of the linux-22.214.171.124 sources (sorry, untimed) , and timing the git commit.
Mo betta data latah.
Mike Taht wrote:
I started rolling a tool to measure various aspects of git performance. I will start looking at merge next, and at workloads different from the kernel (gcc4 anyone?) ...
The only data points worth sharing a this point are:
That doing the compression at a level of 3, rather than the max of 9, cuts the cpu time required for a big git commit by over half, and that that actually translates into a win on the I/O to disk. (these tests were performed on a dual opteron 842)
The benefits of compression aren't very much for git right now.
And: A big git commit is I/O bound. But we knew that. Maybe it's possible to make it less I/O bound.
Git branch: 7a4c67965de68ae7bc7aa1fde33f8eb9d8114697 Tree: 126.96.36.199 source tree Branch: N/a Merge File: N/a HW: dual opteron 242 Mem: 1GB Disk: seagate barracuda Filesystem: Reiser3 Git add: N/a Cache: Hot Git Commit: 44.97user 5.94system 1:45.24elapsed 48%CPU Git Merge: Options: Feature: Test of compression=9 (std git)
du -s .git/objects 110106 # du is probably not the right thing du -s --apparent-size .git/objects 58979
Git branch: 9e272677621c91784cf2533123a41745178f0701 Tree: 188.8.131.52 source tree Branch: N/a Merge File: N/a HW: dual opteron 242 Mem: 1GB Disk: seagate barracuda Disk mode: udma5 Filesystem: Reiser3 Git add: N/a Cache: Hot Git Commit: 16.79user 6.15system 1:21.92elapsed 28%CPU Git Merge: Options: Feature: Test of compression=3 (std git)
du -s .git/objects 115218 du -s --apparent-size .git/objects 64274
There's some variety in the best/worst case timings for I/O for the compressor=3 case...
16.79user 6.15system 1:21.92elapsed 28%CPU 16.68user 5.71system 1:13.19elapsed 30%CPU
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