This trivial 256-entry delta_base cache improves performance for some
loads by a factor of 2.5 or so.
Instead of always re-generating the delta bases (possibly over and over
and over again), just cache the last few ones. They often can get re-used.
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
---
This should have some other people doing performance testing too, since
it's fairly core. But *dang*, it's really simple.
diff --git a/sha1_file.c b/sha1_file.c
index f11ca3f..a7e3a2a 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -1352,16 +1352,57 @@ static void *unpack_compressed_entry(struct packed_git *p,
return buffer;
}
+#define MAX_DELTA_CACHE (256)
+
+static struct delta_base_cache_entry {
+ struct packed_git *p;
+ off_t base_offset;
+ unsigned long size;
+ void *data;
+ enum object_type type;
+} delta_base_cache[MAX_DELTA_CACHE];
+
+static unsigned long pack_entry_hash(struct packed_git *p, off_t base_offset)
+{
+ unsigned long hash;
+
+ hash = (unsigned long)p + (unsigned long)base_offset;
+ hash += (hash >> 8) + (hash >> 16);
+ return hash & 0xff;
+}
+
static void *cache_or_unpack_entry(struct packed_git *p, off_t base_offset,
unsigned long *base_size, enum object_type *type)
{
+ void *ret;
+ unsigned long hash = pack_entry_hash(p, base_offset);
+ struct delta_base_cache_entry *ent = delta_base_cache + hash;
+
+ ret = ent->data;
+ if (ret && ent->p == p && ent->base_offset == base_offset)
+ goto found_cache_entry;
return unpack_entry(p, base_offset, type, base_size);
+
+found_cache_entry:
+ ent->data = NULL;
+ *type = ent->type;
+ *base_size = ent->size;
+ return ret;
}
static void add_delta_base_cache(struct packed_git *p, off_t base_offset,
void *base, unsigned long base_size, enum object_type type)
{
- free(base);
+ unsigned long hash = pack_entry_hash(p, base_offset);
+ struct delta_base_cache_entry *ent = delta_base_cache + hash;
+
+ if (ent->data)
+ free(ent->data);
+ ent->p = p;
+ ent->base_offset = base_offset;
+ ent->type = type;
+ ent->data = base;
+ ent->size = base_size;
}
static void *unpack_delta_entry(struct packed_git *p,
-
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