From e5e01619bcb753a3c45fb51d498371c9ff0677da Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 17 Mar 2007 12:44:06 -0700 Subject: [PATCH] Implement a simple delta_base cache 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 Signed-off-by: Junio C Hamano --- sha1_file.c | 43 ++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 42 insertions(+), 1 deletion(-) diff --git a/sha1_file.c b/sha1_file.c index f11ca3fbac..a7e3a2a9f9 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, -- 2.43.2