This patch helps address the CPU cost of loading the index by loading
the cache extensions on a worker thread in parallel with loading the cache
entries.
This is possible because the current extensions don't access the cache
entries in the index_state structure so are OK that they don't all exist
yet.
The CACHE_EXT_TREE, CACHE_EXT_RESOLVE_UNDO, and CACHE_EXT_UNTRACKED
extensions don't even get a pointer to the index so don't have access to the
cache entries.
CACHE_EXT_LINK only uses the index_state to initialize the split index.
CACHE_EXT_FSMONITOR only uses the index_state to save the fsmonitor last
update and dirty flags.
I used p0002-read-cache.sh to generate some performance data on the
cumulative impact:
100,000 entries
Test HEAD~3 HEAD~2
---------------------------------------------------------------------------
read_cache/discard_cache 1000 times 14.08(0.01+0.10) 9.72(0.03+0.06) -31.0%
1,000,000 entries
Test HEAD~3 HEAD~2
------------------------------------------------------------------------------
read_cache/discard_cache 1000 times 202.95(0.01+0.07) 154.14(0.03+0.06) -24.1%
Signed-off-by: Ben Peart <Ben.Peart@xxxxxxxxxxxxx>
---
read-cache.c | 60 +++++++++++++++++++++++++++++++++++++++++-----------
1 file changed, 48 insertions(+), 12 deletions(-)
diff --git a/read-cache.c b/read-cache.c
index c30346388a..f768004617 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -1959,16 +1959,13 @@ struct load_cache_entries_thread_data
struct mem_pool *ce_mem_pool;
int offset, nr;
void *mmap;
+ size_t mmap_size;
unsigned long start_offset;
struct strbuf previous_name_buf;
struct strbuf *previous_name;
unsigned long consumed; /* return # of bytes in index file processed */
};
-/*
-* A thread proc to run the load_cache_entries() computation
-* across multiple background threads.
-*/
static void *load_cache_entries_thread(void *_data)
{
struct load_cache_entries_thread_data *p = _data;
@@ -1978,6 +1975,36 @@ static void *load_cache_entries_thread(void *_data)
return NULL;
}
+static void *load_index_extensions_thread(void *_data)
+{
+ struct load_cache_entries_thread_data *p = _data;
+ unsigned long src_offset = p->start_offset;
+
+ while (src_offset <= p->mmap_size - the_hash_algo->rawsz - 8) {
+ /* After an array of active_nr index entries,
+ * there can be arbitrary number of extended
+ * sections, each of which is prefixed with
+ * extension name (4-byte) and section length
+ * in 4-byte network byte order.
+ */
+ uint32_t extsize;
+ memcpy(&extsize, (char *)p->mmap + src_offset + 4, 4);
+ extsize = ntohl(extsize);
+ if (read_index_extension(p->istate,
+ (const char *)p->mmap + src_offset,
+ (char *)p->mmap + src_offset + 8,
+ extsize) < 0) {
+ munmap(p->mmap, p->mmap_size);
+ die("index file corrupt");
+ }
+ src_offset += 8;
+ src_offset += extsize;
+ }
+ p->consumed += src_offset - p->start_offset;
+
+ return NULL;
+}
+
static unsigned long load_cache_entries(struct index_state *istate,
void *mmap, size_t mmap_size, unsigned long src_offset)
{
@@ -2012,16 +2039,16 @@ static unsigned long load_cache_entries(struct index_state *istate,
else
previous_name = NULL;
+ /* allocate an extra thread for loading the index extensions */
ce_per_thread = DIV_ROUND_UP(istate->cache_nr, nr_threads);
- data = xcalloc(nr_threads, sizeof(struct load_cache_entries_thread_data));
+ data = xcalloc(nr_threads + 1, sizeof(struct load_cache_entries_thread_data));
/*
* Loop through index entries starting a thread for every ce_per_thread
- * entries. Exit the loop when we've created the final thread (no need
- * to parse the remaining entries.
+ * entries.
*/
consumed = thread = 0;
- for (i = 0; ; i++) {
+ for (i = 0; i < istate->cache_nr; i++) {
struct ondisk_cache_entry *ondisk;
const char *name;
unsigned int flags;
@@ -2055,9 +2082,7 @@ static unsigned long load_cache_entries(struct index_state *istate,
if (pthread_create(&p->pthread, NULL, load_cache_entries_thread, p))
die("unable to create load_cache_entries_thread");
- /* exit the loop when we've created the last thread */
- if (++thread == nr_threads)
- break;
+ ++thread;
}
ondisk = (struct ondisk_cache_entry *)((char *)mmap + src_offset);
@@ -2086,7 +2111,18 @@ static unsigned long load_cache_entries(struct index_state *istate,
src_offset += (name - ((char *)ondisk)) + expand_name_field(previous_name, name);
}
- for (i = 0; i < nr_threads; i++) {
+ /* create a thread to load the index extensions */
+ struct load_cache_entries_thread_data *p = &data[thread];
+ p->istate = istate;
+ mem_pool_init(&p->ce_mem_pool, 0);
+ p->mmap = mmap;
+ p->mmap_size = mmap_size;
+ p->start_offset = src_offset;
+
+ if (pthread_create(&p->pthread, NULL, load_index_extensions_thread, p))
+ die("unable to create load_index_extensions_thread");
+
+ for (i = 0; i < nr_threads + 1; i++) {
struct load_cache_entries_thread_data *p = data + i;
if (pthread_join(p->pthread, NULL))
die("unable to join load_cache_entries_thread");
--
2.18.0.windows.1
