From b3373982667dc983b8dacf33861d25b20bafb995 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Thu, 1 Apr 2010 20:14:24 -0400 Subject: [PATCH] diff: avoid useless filespec population builtin_diff calls fill_mmfile fairly early, which in turn calls diff_populate_filespec, which actually retrieves the file's blob contents into a buffer. Long ago, this was sensible as we would need to look at the blobs eventually. These days, however, we may not ever want those blobs if we end up using a textconv cache, and for large binary files (exactly the sort for which you might have a textconv cache), just retrieving the objects can be costly. This patch just pushes the fill_mmfile call a bit later, so we can avoid populating the filespec in some cases. There is one thing to note that looks like a bug but isn't. We push the fill_mmfile down into the first branch of a conditional. It seems like we would need it on the other branch, too, but we don't; fill_textconv does it for us (in fact, before this, we were just writing over the results of the fill_mmfile on that branch). Here's a timing sample on a commit with 45 changed jpgs and avis. The result is fully textconv cached, but we still wasted a lot of time just pulling the blobs from storage. The total size of the blobs (source and dest) is about 180M. [before] $ time git show >/dev/null real 0m0.352s user 0m0.148s sys 0m0.200s [after] $ time git show >/dev/null real 0m0.009s user 0m0.004s sys 0m0.004s And that's on a warm cache. On a cold cache, the "after" case is not much worse, but the "before" case has to do an extra 180M of I/O. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- diff.c | 9 ++++----- 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/diff.c b/diff.c index 72d8503d89..4cb6d9a9e8 100644 --- a/diff.c +++ b/diff.c @@ -1680,12 +1680,11 @@ static void builtin_diff(const char *name_a, } } - if (fill_mmfile(&mf1, one) < 0 || fill_mmfile(&mf2, two) < 0) - die("unable to read files to diff"); - if (!DIFF_OPT_TST(o, TEXT) && - ( (diff_filespec_is_binary(one) && !textconv_one) || - (diff_filespec_is_binary(two) && !textconv_two) )) { + ( (!textconv_one && diff_filespec_is_binary(one)) || + (!textconv_two && diff_filespec_is_binary(two)) )) { + if (fill_mmfile(&mf1, one) < 0 || fill_mmfile(&mf2, two) < 0) + die("unable to read files to diff"); /* Quite common confusing case */ if (mf1.size == mf2.size && !memcmp(mf1.ptr, mf2.ptr, mf1.size))