Am 11.08.2018 um 22:59 schrieb René Scharfe:
If the current oidset implementation is so bad, why not replace it with
one based on oid_array? ;-)
Intuitively I'd try a hashmap with no payload and open addressing via
sha1hash(), which should reduce memory allocations quite a bit -- no
need to store hash codes and next pointers, only an array of object IDs
with a fill rate of 50% or so. Deletions are a bit awkward with that
scheme, though; they could perhaps be implemented as insertions into a
second hashmap.
Here's roughly what I had in mind, only with a free/occupied bitmap (or
a one-bit payload, if you will). I tried a variant that encoded empty
slots as null_oid first, which has lower memory usage, but isn't any
faster than the current code.
# in git.git
$ hyperfine "./git-cat-file --batch-all-objects --buffer --unordered --batch-check='%(objectname)'"
Before:
Benchmark #1: ./git-cat-file --batch-all-objects --buffer --unordered --batch-check='%(objectname)'
Time (mean ± σ): 269.5 ms ± 26.7 ms [User: 247.7 ms, System: 21.4 ms]
Range (min … max): 240.3 ms … 339.3 ms
After:
Benchmark #1: ./git-cat-file --batch-all-objects --buffer --unordered --batch-check='%(objectname)'
Time (mean ± σ): 224.2 ms ± 18.2 ms [User: 201.7 ms, System: 22.1 ms]
Range (min … max): 205.0 ms … 259.0 ms
So that's only slightly faster. :-|
---
builtin/cat-file.c | 93 +++++++++++++++++++++++++++++++++++++++++++---
1 file changed, 88 insertions(+), 5 deletions(-)
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 45992c9be9..b197cca861 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -408,10 +408,93 @@ static void batch_one_object(const char *obj_name, struct batch_options *opt,
batch_object_write(obj_name, opt, data);
}
+struct oidset2 {
+ size_t nr, alloc;
+ struct object_id *entries;
+ uint32_t *bitmap;
+};
+
+static int is_bit_set(const uint32_t *bitmap, size_t idx)
+{
+ uint32_t mask = 1 << (idx % bitsizeof(bitmap[0]));
+ return bitmap[idx / bitsizeof(bitmap[0])] & mask;
+}
+
+static void set_bit(uint32_t *bitmap, size_t idx)
+{
+ uint32_t mask = 1 << (idx % bitsizeof(bitmap[0]));
+ bitmap[idx / bitsizeof(bitmap[0])] |= mask;
+}
+
+static void oidset2_add(struct oidset2 *set, const struct object_id *oid)
+{
+ size_t idx;
+
+ for (idx = sha1hash(oid->hash) % set->alloc;;) {
+ if (!is_bit_set(set->bitmap, idx))
+ break;
+ if (!oidcmp(&set->entries[idx], oid))
+ return;
+ if (++idx >= set->alloc)
+ idx = 0;
+ }
+ oidcpy(&set->entries[idx], oid);
+ set_bit(set->bitmap, idx);
+ set->nr++;
+}
+
+static void oidset2_grow(struct oidset2 *set)
+{
+ struct oidset2 old_set = *set;
+ size_t idx;
+
+ set->alloc = (old_set.alloc + 1000) * 3 / 2;
+ set->nr = 0;
+ set->entries = xcalloc(set->alloc, sizeof(set->entries[0]));
+ set->bitmap = xcalloc(set->alloc / 32 + 1, sizeof(set->bitmap[0]));
+ for (idx = 0; idx < old_set.alloc; idx++) {
+ if (!is_bit_set(old_set.bitmap, idx))
+ continue;
+ oidset2_add(set, &old_set.entries[idx]);
+ }
+ free(old_set.entries);
+ free(old_set.bitmap);
+}
+
+static void oidset2_insert(struct oidset2 *set, const struct object_id *oid)
+{
+ if (set->nr + 1 > set->alloc * 2 / 3)
+ oidset2_grow(set);
+ oidset2_add(set, oid);
+}
+
+static int oidset2_contains(struct oidset2 *set, const struct object_id *oid)
+{
+ size_t idx;
+
+ if (!set->nr)
+ return 0;
+ for (idx = sha1hash(oid->hash) % set->alloc;;) {
+ if (!is_bit_set(set->bitmap, idx))
+ return 0;
+ if (!oidcmp(&set->entries[idx], oid))
+ return 1;
+ if (++idx >= set->alloc)
+ idx = 0;
+ }
+}
+
+static void oidset2_clear(struct oidset2 *set)
+{
+ FREE_AND_NULL(set->entries);
+ FREE_AND_NULL(set->bitmap);
+ set->alloc = set->nr = 0;
+}
+
struct object_cb_data {
struct batch_options *opt;
struct expand_data *expand;
- struct oidset *seen;
+ struct oidset2 *seen;
};
static int batch_object_cb(const struct object_id *oid, void *vdata)
@@ -443,9 +526,9 @@ static int batch_unordered_object(const struct object_id *oid, void *vdata)
{
struct object_cb_data *data = vdata;
- if (oidset_contains(data->seen, oid))
+ if (oidset2_contains(data->seen, oid))
return 0;
- oidset_insert(data->seen, oid);
+ oidset2_insert(data->seen, oid);
return batch_object_cb(oid, data);
}
@@ -510,7 +593,7 @@ static int batch_objects(struct batch_options *opt)
cb.expand = &data;
if (opt->unordered) {
- struct oidset seen = OIDSET_INIT;
+ struct oidset2 seen = { 0 };
cb.seen = &seen;
@@ -518,7 +601,7 @@ static int batch_objects(struct batch_options *opt)
for_each_packed_object(batch_unordered_packed, &cb,
FOR_EACH_OBJECT_PACK_ORDER);
- oidset_clear(&seen);
+ oidset2_clear(&seen);
} else {
struct oid_array sa = OID_ARRAY_INIT;
--
2.18.0
