From b72a1904aefb9e27014a11790f3af4dc90b38e8d Mon Sep 17 00:00:00 2001 From: Jeff King Date: Fri, 13 Jul 2012 03:50:23 -0400 Subject: [PATCH] revision: avoid work after --max-count is reached During a revision traversal in which --max-count has been specified, we decrement a counter for each revision returned by get_revision. When it hits 0, we typically return NULL (the exception being if we still have boundary commits to show). However, before we check the counter, we call get_revision_1 to get the next commit. This might involve looking at a large number of commits if we have restricted the traversal (e.g., we might traverse until we find the next commit whose diff actually matches a pathspec). There's no need to make this get_revision_1 call when our counter runs out. If we are not in --boundary mode, we will just throw away the result and immediately return NULL. If we are in --boundary mode, then we will still throw away the result, and then start showing the boundary commits. However, as git_revision_1 does not impact the boundary list, it should not have an impact. In most cases, avoiding this work will not be especially noticeable. However, in some cases, it can make a big difference: [before] $ time git rev-list -1 origin Documentation/RelNotes/1.7.11.2.txt 8d141a1d562abb31f27f599dbf6e10a6c06ed73e real 0m0.301s user 0m0.280s sys 0m0.016s [after] $ time git rev-list -1 origin Documentation/RelNotes/1.7.11.2.txt 8d141a1d562abb31f27f599dbf6e10a6c06ed73e real 0m0.010s user 0m0.008s sys 0m0.000s Note that the output is produced almost instantaneously in the first case, and then git uselessly spends a long time looking for the next commit to touch that file (but there isn't one, and we traverse all the way down to the roots). Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- revision.c | 39 +++++++++++++++++++-------------------- 1 file changed, 19 insertions(+), 20 deletions(-) diff --git a/revision.c b/revision.c index 5b81a92e3..7e3965557 100644 --- a/revision.c +++ b/revision.c @@ -2361,29 +2361,28 @@ static struct commit *get_revision_internal(struct rev_info *revs) } /* - * Now pick up what they want to give us + * If our max_count counter has reached zero, then we are done. We + * don't simply return NULL because we still might need to show + * boundary commits. But we want to avoid calling get_revision_1, which + * might do a considerable amount of work finding the next commit only + * for us to throw it away. + * + * If it is non-zero, then either we don't have a max_count at all + * (-1), or it is still counting, in which case we decrement. */ - c = get_revision_1(revs); - if (c) { - while (0 < revs->skip_count) { - revs->skip_count--; - c = get_revision_1(revs); - if (!c) - break; + if (revs->max_count) { + c = get_revision_1(revs); + if (c) { + while (0 < revs->skip_count) { + revs->skip_count--; + c = get_revision_1(revs); + if (!c) + break; + } } - } - /* - * Check the max_count. - */ - switch (revs->max_count) { - case -1: - break; - case 0: - c = NULL; - break; - default: - revs->max_count--; + if (revs->max_count > 0) + revs->max_count--; } if (c) -- 2.26.2