[PATCH v4 13/23] rev-list: add bitmap mode to speed up object lists
- From
Jeff King <peff@peff.net>
- Date
- Dec 21, 2013, 14:00 UTC
- Message-ID
- <20131221140012.GM21145@sigill.intra.peff.net>
- In-Reply-To
- <20131221135651.GA20818@sigill.intra.peff.net>
From: Vicent Marti <tanoku@gmail.com>
The bitmap reachability index used to speed up the counting objects phase during `pack-objects` can also be used to optimize a normal rev-list if the only thing required are the SHA1s of the objects during the list (i.e., not the path names at which trees and blobs were found).
Calling `git rev-list --objects --use-bitmap-index [committish]` will perform an object iteration based on a bitmap result instead of actually walking the object graph.
These are some example timings for `torvalds/linux` (warm cache, best-of-five):
$ time git rev-list --objects master > /dev/null
real 0m34.191s
user 0m33.904s
sys 0m0.268s$ time git rev-list --objects --use-bitmap-index master > /dev/null
real 0m1.041s
user 0m0.976s
sys 0m0.064sLikewise, using `git rev-list --count --use-bitmap-index` will speed up the counting operation by building the resulting bitmap and performing a fast popcount (number of bits set on the bitmap) on the result.
Here are some sample timings of different ways to count commits in `torvalds/linux`:
$ time git rev-list master | wc -l
399882 real 0m6.524s
user 0m6.060s
sys 0m3.284s $ time git rev-list --count master
399882 real 0m4.318s
user 0m4.236s
sys 0m0.076s $ time git rev-list --use-bitmap-index --count master
399882 real 0m0.217s
user 0m0.176s
sys 0m0.040sThis also respects negative refs, so you can use it to count a slice of history:
$ time git rev-list --count v3.0..master
144843 real 0m1.971s
user 0m1.932s
sys 0m0.036s $ time git rev-list --use-bitmap-index --count v3.0..master
real 0m0.280s
user 0m0.220s
sys 0m0.056sThough note that the closer the endpoints, the less it helps. In the traversal case, we have fewer commits to cross, so we take less time. But the bitmap time is dominated by generating the pack revindex, which is constant with respect to the refs given.
Note that you cannot yet get a fast --left-right count of a symmetric difference (e.g., "--count --left-right master...topic"). The slow part of that walk actually happens during the merge-base determination when we parse "master...topic". Even though a count does not actually need to know the real merge base (it only needs to take the symmetric difference of the bitmaps), the revision code would require some refactoring to handle this case.
Additionally, a `--test-bitmap` flag has been added that will perform the same rev-list manually (i.e. using a normal revwalk) and using bitmaps, and verify that the results are the same. This can be used to exercise the bitmap code, and also to verify that the contents of the .bitmap file are sane.
Signed-off-by: Vicent Marti <tanoku@gmail.com> Signed-off-by: Jeff King <peff@peff.net> --- Documentation/git-rev-list.txt | 1 + Documentation/rev-list-options.txt | 8 ++++++++ builtin/rev-list.c | 39 ++++++++++++++++++++++++++++++++++++++ 3 files changed, 48 insertions(+)
diff --git a/Documentation/git-rev-list.txt b/Documentation/git-rev-list.txt index 045b37b..7a1585d 100644 --- a/Documentation/git-rev-list.txt +++ b/Documentation/git-rev-list.txt @@ -55,6 +55,7 @@ SYNOPSIS [ \--reverse ] [ \--walk-reflogs ] [ \--no-walk ] [ \--do-walk ] + [ \--use-bitmap-index ] <commit>... [ \-- <paths>... ] DESCRIPTION diff --git a/Documentation/rev-list-options.txt b/Documentation/rev-list-options.txt index 5bdfb42..c236b85 100644 --- a/Documentation/rev-list-options.txt +++ b/Documentation/rev-list-options.txt @@ -274,6 +274,14 @@ See also linkgit:git-reflog[1]. Output excluded boundary commits. Boundary commits are prefixed with `-`. +ifdef::git-rev-list[] +--use-bitmap-index:: + + Try to speed up the traversal using the pack bitmap index (if + one is available). Note that when traversing with `--objects`, + trees and blobs will not have their associated path printed. +endif::git-rev-list[] + -- History Simplification diff --git a/builtin/rev-list.c b/builtin/rev-list.c index 4fc1616..5209255 100644 --- a/builtin/rev-list.c +++ b/builtin/rev-list.c @@ -3,6 +3,8 @@ #include "diff.h" #include "revision.h" #include "list-objects.h" +#include "pack.h" +#include "pack-bitmap.h" #include "builtin.h" #include "log-tree.h" #include "graph.h" @@ -257,6 +259,18 @@ static int show_bisect_vars(struct rev_list_info *info, int reaches, int all) return 0; } +static int show_object_fast( + const unsigned char *sha1, + enum object_type type, + int exclude, + uint32_t name_hash, + struct packed_git *found_pack, + off_t found_offset) +{ + fprintf(stdout, "%s\n", sha1_to_hex(sha1)); + return 1; +} + int cmd_rev_list(int argc, const char **argv, const char *prefix) { struct rev_info revs; @@ -265,6 +279,7 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix) int bisect_list = 0; int bisect_show_vars = 0; int bisect_find_all = 0; + int use_bitmap_index = 0; git_config(git_default_config, NULL); init_revisions(&revs, prefix); @@ -306,6 +321,14 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix) bisect_show_vars = 1; continue; } + if (!strcmp(arg, "--use-bitmap-index")) { + use_bitmap_index = 1; + continue; + } + if (!strcmp(arg, "--test-bitmap")) { + test_bitmap_walk(&revs); + return 0; + } usage(rev_list_usage); } @@ -333,6 +356,22 @@ int cmd_rev_list(int argc, const char **argv, const char *prefix) if (bisect_list) revs.limited = 1; + if (use_bitmap_index) { + if (revs.count && !revs.left_right && !revs.cherry_mark) { + uint32_t commit_count; + if (!prepare_bitmap_walk(&revs)) { + count_bitmap_commit_list(&commit_count, NULL, NULL, NULL); + printf("%d\n", commit_count); + return 0; + } + } else if (revs.tag_objects && revs.tree_objects && revs.blob_objects) { + if (!prepare_bitmap_walk(&revs)) { + traverse_bitmap_commit_list(&show_object_fast); + return 0; + } + } + } + if (prepare_revision_walk(&revs)) die("revision walk setup failed"); if (revs.tree_objects)
-- 1.8.5.1.399.g900e7cd