On Wed, May 01, 2013 at 04:49:47PM -0400, Jeff King wrote:
> Another avenue I'd like to explore is actually doing a tree-diff from
> the last processed commit, since we should need to examine only the
> changed entries. I suspect it won't be a big benefit, though, because
> even though the tree diff can happen in O(# of entries), we are trying
> to beat doing an O(1) hash for each entry. So it's the same algorithmic
> complexity, and it is hard to beat a few hashcmp() calls. We'll see.
As I suspected, this is not a win:
Test origin this tree
--------------------------------------------------------------------------
0001.1: rev-list --all 0.40(0.37+0.02) 0.40(0.38+0.01) +0.0%
0001.2: rev-list --all --objects 2.22(2.16+0.05) 2.41(2.16+0.24) +8.6%
I've included the patch below for reference. It really does work as
planned; the number of calls to lookup_object for doing "rev-list --all
--objects" on git.git is reduced from ~15M to ~2.6M. But the benefit is
eaten up by the extra tree-processing time. For fun, here's an excerpt
from the "perf diff" between the two versions:
+10.51% git [.] update_tree_entry
+8.97% git [.] lookup_object
+7.81% git [.] process_tree
+5.20% libc-2.13.so [.] __memcmp_sse4_1
+3.77% libc-2.13.so [.] __strlen_sse42
+2.69% git [.] base_name_compare
[....]
-7.90% git [.] tree_entry
-39.19% git [.] lookup_object
Shawn had suggested trying to store the tree deltas in such a way that
these tree comparisons could be done more cheaply. That might tip things
in favor of the tree-diff approach.
-Peff
---
diff --git a/list-objects.c b/list-objects.c
index 3dd4a96..b87a049 100644
--- a/list-objects.c
+++ b/list-objects.c
@@ -59,8 +59,57 @@ static void process_tree(struct rev_info *revs,
/* Nothing to do */
}
+static struct tree *skip_processed_entries(struct tree_desc *cur,
+ struct tree_desc *old)
+{
+ while (cur->size && old->size) {
+ int cmp = base_name_compare(cur->entry.path,
+ tree_entry_len(&cur->entry),
+ 0, /* ignore mode */
+ old->entry.path,
+ tree_entry_len(&old->entry),
+ 0);
+ if (cmp > 0) {
+ /*
+ * Old tree has something we do not; ignore it, as it
+ * was already processed.
+ */
+ update_tree_entry(old);
+ }
+ else if (cmp == 0) {
+ /*
+ * We have the same path; if the sha1s match, then we
+ * have already processed it and can ignore. Otherwise,
+ * return for processing, but also provide the old
+ * tree so that we can recurse.
+ */
+ if (!hashcmp(cur->entry.sha1, old->entry.sha1)) {
+ update_tree_entry(cur);
+ update_tree_entry(old);
+ }
+ else {
+ struct object *o =
lookup_object(old->entry.sha1);
+ update_tree_entry(old);
+ if (o && o->type == OBJ_TREE)
+ return (struct tree *)o;
+ else
+ return NULL;
+ }
+ }
+ else {
+ /*
+ * We have an entry the old one does not; we must look
+ * at it (and there is no matching old tree to report).
+ */
+ return NULL;
+ }
+ }
+ return NULL;
+}
+
static void process_tree(struct rev_info *revs,
struct tree *tree,
+ struct tree *old_tree,
show_object_fn show,
struct name_path *path,
struct strbuf *base,
@@ -68,7 +117,7 @@ static void process_tree(struct rev_info *revs,
void *cb_data)
{
struct object *obj = &tree->object;
- struct tree_desc desc;
+ struct tree_desc desc, old_desc;
struct name_entry entry;
struct name_path me;
enum interesting match = revs->diffopt.pathspec.nr == 0 ?
@@ -97,7 +146,18 @@ static void process_tree(struct rev_info *revs,
init_tree_desc(&desc, tree->buffer, tree->size);
- while (tree_entry(&desc, &entry)) {
+ if (old_tree)
+ init_tree_desc(&old_desc, old_tree->buffer, old_tree->size);
+ else
+ init_tree_desc(&old_desc, NULL, 0);
+
+ while (desc.size) {
+ struct tree *old_tree;
+
+ old_tree = skip_processed_entries(&desc, &old_desc);
+ if (!tree_entry(&desc, &entry))
+ break;
+
if (match != all_entries_interesting) {
match = tree_entry_interesting(&entry, base, 0,
&revs->diffopt.pathspec);
@@ -109,7 +169,7 @@ static void process_tree(struct rev_info *revs,
if (S_ISDIR(entry.mode))
process_tree(revs,
- lookup_tree(entry.sha1),
+ lookup_tree(entry.sha1), old_tree,
show, &me, base, entry.path,
cb_data);
else if (S_ISGITLINK(entry.mode))
@@ -123,8 +183,6 @@ static void process_tree(struct rev_info *revs,
cb_data);
}
strbuf_setlen(base, baselen);
- free(tree->buffer);
- tree->buffer = NULL;
}
static void mark_edge_parents_uninteresting(struct commit *commit,
@@ -173,6 +231,7 @@ void traverse_commit_list(struct rev_info *revs,
int i;
struct commit *commit;
struct strbuf base;
+ struct tree *last_root_tree = NULL;
strbuf_init(&base, PATH_MAX);
while ((commit = get_revision(revs)) != NULL) {
@@ -196,8 +255,9 @@ void traverse_commit_list(struct rev_info *revs,
continue;
}
if (obj->type == OBJ_TREE) {
- process_tree(revs, (struct tree *)obj, show_object,
- NULL, &base, name, data);
+ process_tree(revs, (struct tree *)obj, last_root_tree,
+ show_object, NULL, &base, name, data);
+ last_root_tree = (struct tree *)obj;
continue;
}
if (obj->type == OBJ_BLOB) {
--
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