Add cache preload facility

This can do the lstat() storm in parallel, giving potentially much
improved performance for cold-cache cases or things like NFS that have
weak metadata caching.

Just use "read_cache_preload()" instead of "read_cache()" to force an
optimistic preload of the index stat data.  The function takes a
pathspec as its argument, allowing us to preload only the relevant
portion of the index.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/builtin-diff-files.c b/builtin-diff-files.c
index 2b578c714..5b64011de 100644
--- a/builtin-diff-files.c
+++ b/builtin-diff-files.c
@@ -59,8 +59,8 @@ int cmd_diff_files(int argc, const char **argv, const char *prefix)
 	    (rev.diffopt.output_format & DIFF_FORMAT_PATCH))
 		rev.combine_merges = rev.dense_combined_merges = 1;
 
-	if (read_cache() < 0) {
-		perror("read_cache");
+	if (read_cache_preload(rev.diffopt.paths) < 0) {
+		perror("read_cache_preload");
 		return -1;
 	}
 	result = run_diff_files(&rev, options);