On Thu, 14 Aug 2008, Linus Torvalds wrote:
>
> So yeah, trees are the problem here, and yes, avoiding inflating them
> would help - but mainly because we do it something like four times per
> object on average!
Interestingly, it turns out that git also hits a sad performance downside
of using zlib.
We always tend to set "stream.avail_out" to the exact size of the expected
output. And it turns out that that means that the fast-path case of
inffast.c doesn't trigger as often as it could. This (idiotic) patch
actually seems to help performance on git rev-list by about 5%.
But maybe it's just me seeing things. But I did this because of the entry
assumptions in inflate_fast(), that code only triggers for the case of
strm->avail_out >= 258.
Sad, if true.
Linus
---
sha1_file.c | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/sha1_file.c b/sha1_file.c
index a57155d..5ca7ce2 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1500,11 +1500,11 @@ static void *unpack_compressed_entry(struct packed_git *p,
z_stream stream;
unsigned char *buffer, *in;
- buffer = xmalloc(size + 1);
+ buffer = xmalloc(size + 256 + 1);
buffer[size] = 0;
memset(&stream, 0, sizeof(stream));
stream.next_out = buffer;
- stream.avail_out = size;
+ stream.avail_out = size + 256;
inflateInit(&stream);
do {
--
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