[PATCH v2 7/7] unpack-trees: improve performance of next_cache_entry
- From
Victoria Dye via GitGitGadget <gitgitgadget@gmail.com>
- Date
- Oct 5, 2021, 13:20 UTC
- Message-ID
- <aa963eefae75d41983201e24398bc5692267b91b.1633440057.git.gitgitgadget@gmail.com>
- In-Reply-To
- <pull.1048.v2.git.1633440057.gitgitgadget@gmail.com>
From: Victoria Dye <vdye@github.com>
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. The performance of `git reset -- does-not-exist` (testing the "worst case" in which all entries in the index are unpacked with `next_cache_entry`) is significantly improved for the sparse index case:
Test before after ------------------------------------------------------ (full-v3) 0.79(0.38+0.30) 0.91(0.43+0.34) +15.2% (full-v4) 0.80(0.38+0.29) 0.85(0.40+0.35) +6.2% (sparse-v3) 0.76(0.43+0.69) 0.44(0.08+0.67) -42.1% (sparse-v4) 0.71(0.40+0.65) 0.41(0.09+0.65) -42.3%
Signed-off-by: Victoria Dye <vdye@github.com> --- unpack-trees.c | 23 +++++++++++++++++------ 1 file changed, 17 insertions(+), 6 deletions(-)
diff --git a/unpack-trees.c b/unpack-trees.c index 8ea0a542da8..b94733de6be 100644 --- a/unpack-trees.c +++ b/unpack-trees.c @@ -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)
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