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unpack-trees: improve performance of next_cache_entry 

To find the first non-unpacked cache entry, `next_cache_entry` iterates
through index, starting at `cache_bottom`. The performance of this in full
indexes is helped by `cache_bottom` advancing with each invocation of
`mark_ce_used` (called by `unpack_index_entry`). However, the presence of
sparse directories can prevent the `cache_bottom` from advancing in a sparse
index case, effectively forcing `next_cache_entry` to search from the
beginning of the index each time it is called.

The `cache_bottom` must be preserved for the sparse index (see 17a1bb570b
(unpack-trees: preserve cache_bottom, 2021-07-14)). Therefore, to retain the
benefit `cache_bottom` provides in non-sparse index cases, a separate `hint`
position indicates the first position `next_cache_entry` should search,
updated each execution with a new position.

Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Victoria Dye 2021-11-29 15:52:43 +00:00 committed by Junio C Hamano
parent 4d1cfc1351
commit f2a454e0a5
1 changed files with 17 additions and 6 deletions
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23
unpack-trees.c
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@ -645,17 +645,24 @@ static void mark_ce_used_same_name(struct cache_entry *ce,
}
}
static struct cache_entry *next_cache_entry(struct unpack_trees_options *o)
static struct cache_entry *next_cache_entry(struct unpack_trees_options *o, int *hint)
{
const struct index_state *index = o->src_index;
int pos = o->cache_bottom;
if (*hint > pos)
pos = *hint;
while (pos < index->cache_nr) {
struct cache_entry *ce = index->cache[pos];
if (!(ce->ce_flags & CE_UNPACKED))
if (!(ce->ce_flags & CE_UNPACKED)) {
*hint = pos + 1;
return ce;
}
pos++;
}
*hint = pos;
return NULL;
}
@ -1365,12 +1372,13 @@ static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, str
/* Are we supposed to look at the index too? */
if (o->merge) {
int hint = -1;
while (1) {
int cmp;
struct cache_entry *ce;
if (o->diff_index_cached)
ce = next_cache_entry(o);
ce = next_cache_entry(o, &hint);
else
ce = find_cache_entry(info, p);
@ -1690,7 +1698,7 @@ static int verify_absent(const struct cache_entry *,
int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options *o)
{
struct repository *repo = the_repository;
int i, ret;
int i, hint, ret;
static struct cache_entry *dfc;
struct pattern_list pl;
int free_pattern_list = 0;
@ -1763,13 +1771,15 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
info.pathspec = o->pathspec;
if (o->prefix) {
hint = -1;
/*
* Unpack existing index entries that sort before the
* prefix the tree is spliced into. Note that o->merge
* is always true in this case.
*/
while (1) {
struct cache_entry *ce = next_cache_entry(o);
struct cache_entry *ce = next_cache_entry(o, &hint);
if (!ce)
break;
if (ce_in_traverse_path(ce, &info))
@ -1790,8 +1800,9 @@ int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options
/* Any left-over entries in the index? */
if (o->merge) {
hint = -1;
while (1) {
struct cache_entry *ce = next_cache_entry(o);
struct cache_entry *ce = next_cache_entry(o, &hint);
if (!ce)
break;
if (unpack_index_entry(ce, o) < 0)