Merge branch 'np/delta'

* np/delta:
  builtin-pack-objects.c: avoid bogus gcc warnings
  threaded delta search: proper locking for cache accounting
  threaded delta search: add pack.threads config variable
  fix threaded delta search locking
  threaded delta search: specify number of threads at run time
  threaded delta search: better chunck split point
  threaded delta search: refine work allocation
  basic threaded delta search
  rearrange delta search progress reporting
  localize window memory usage accounting
  straighten the list of objects to deltify

4 files changed, 256 insertions, 59 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 866e0534b8..015910f27a 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -630,9 +630,17 @@ pack.deltaCacheSize::
 	A value of 0 means no limit. Defaults to 0.
 
 pack.deltaCacheLimit::
-	The maxium size of a delta, that is cached in
+	The maximum size of a delta, that is cached in
 	gitlink:git-pack-objects[1]. Defaults to 1000.
 
+pack.threads::
+	Specifies the number of threads to spawn when searching for best
+	delta matches.  This requires that gitlink:git-pack-objects[1]
+	be compiled with pthreads otherwise this option is ignored with a
+	warning. This is meant to reduce packing time on multiprocessor
+	machines. The required amount of memory for the delta search window
+	is however multiplied by the number of threads.
+
 pull.octopus::
 	The default merge strategy to use when pulling multiple branches
 	at once.
diff --git a/Documentation/git-pack-objects.txt b/Documentation/git-pack-objects.txt
index f8a0be3511..628f296ce1 100644
--- a/Documentation/git-pack-objects.txt
+++ b/Documentation/git-pack-objects.txt
@@ -169,6 +169,14 @@ base-name::
 	length, this option typically shrinks the resulting
 	packfile by 3-5 per-cent.
 
+--threads=<n>::
+	Specifies the number of threads to spawn when searching for best
+	delta matches.  This requires that pack-objects be compiled with
+	pthreads otherwise this option is ignored with a warning.
+	This is meant to reduce packing time on multiprocessor machines.
+	The required amount of memory for the delta search window is
+	however multiplied by the number of threads.
+
 --index-version=<version>[,<offset>]::
 	This is intended to be used by the test suite only. It allows
 	to force the version for the generated pack index, and to force
diff --git a/Makefile b/Makefile
index 78cdaa155b..40567ece14 100644
--- a/Makefile
+++ b/Makefile
@@ -124,6 +124,9 @@ all::
 # If not set it defaults to the bare 'wish'. If it is set to the empty
 # string then NO_TCLTK will be forced (this is used by configure script).
 #
+# Define THREADED_DELTA_SEARCH if you have pthreads and wish to exploit
+# parallel delta searching when packing objects.
+#
 
 GIT-VERSION-FILE: .FORCE-GIT-VERSION-FILE
 	@$(SHELL_PATH) ./GIT-VERSION-GEN
@@ -675,6 +678,11 @@ ifdef NO_MEMMEM
 	COMPAT_OBJS += compat/memmem.o
 endif
 
+ifdef THREADED_DELTA_SEARCH
+	BASIC_CFLAGS += -DTHREADED_DELTA_SEARCH
+	EXTLIBS += -lpthread
+endif
+
 ifeq ($(TCLTK_PATH),)
 NO_TCLTK=NoThanks
 endif
diff --git a/builtin-pack-objects.c b/builtin-pack-objects.c
index e64e3a03a0..a15906bdb2 100644
--- a/builtin-pack-objects.c
+++ b/builtin-pack-objects.c
@@ -15,12 +15,16 @@
 #include "list-objects.h"
 #include "progress.h"
 
+#ifdef THREADED_DELTA_SEARCH
+#include <pthread.h>
+#endif
+
 static const char pack_usage[] = "\
 git-pack-objects [{ -q | --progress | --all-progress }] \n\
 	[--max-pack-size=N] [--local] [--incremental] \n\
 	[--window=N] [--window-memory=N] [--depth=N] \n\
 	[--no-reuse-delta] [--no-reuse-object] [--delta-base-offset] \n\
-	[--non-empty] [--revs [--unpacked | --all]*] [--reflog] \n\
+	[--threads=N] [--non-empty] [--revs [--unpacked | --all]*] [--reflog] \n\
 	[--stdout | base-name] [<ref-list | <object-list]";
 
 struct object_entry {
@@ -68,6 +72,7 @@ static int progress = 1;
 static int window = 10;
 static uint32_t pack_size_limit;
 static int depth = 50;
+static int delta_search_threads = 1;
 static int pack_to_stdout;
 static int num_preferred_base;
 static struct progress progress_state;
@@ -78,7 +83,6 @@ static unsigned long delta_cache_size = 0;
 static unsigned long max_delta_cache_size = 0;
 static unsigned long cache_max_small_delta_size = 1000;
 
-static unsigned long window_memory_usage = 0;
 static unsigned long window_memory_limit = 0;
 
 /*
@@ -1291,6 +1295,31 @@ static int delta_cacheable(unsigned long src_size, unsigned long trg_size,
 	return 0;
 }
 
+#ifdef THREADED_DELTA_SEARCH
+
+static pthread_mutex_t read_mutex = PTHREAD_MUTEX_INITIALIZER;
+#define read_lock()		pthread_mutex_lock(&read_mutex)
+#define read_unlock()		pthread_mutex_unlock(&read_mutex)
+
+static pthread_mutex_t cache_mutex = PTHREAD_MUTEX_INITIALIZER;
+#define cache_lock()		pthread_mutex_lock(&cache_mutex)
+#define cache_unlock()		pthread_mutex_unlock(&cache_mutex)
+
+static pthread_mutex_t progress_mutex = PTHREAD_MUTEX_INITIALIZER;
+#define progress_lock()		pthread_mutex_lock(&progress_mutex)
+#define progress_unlock()	pthread_mutex_unlock(&progress_mutex)
+
+#else
+
+#define read_lock()		(void)0
+#define read_unlock()		(void)0
+#define cache_lock()		(void)0
+#define cache_unlock()		(void)0
+#define progress_lock()		(void)0
+#define progress_unlock()	(void)0
+
+#endif
+
 /*
  * We search for deltas _backwards_ in a list sorted by type and
  * by size, so that we see progressively smaller and smaller files.
@@ -1300,7 +1329,7 @@ static int delta_cacheable(unsigned long src_size, unsigned long trg_size,
  * one.
  */
 static int try_delta(struct unpacked *trg, struct unpacked *src,
-		     unsigned max_depth)
+		     unsigned max_depth, unsigned long *mem_usage)
 {
 	struct object_entry *trg_entry = trg->entry;
 	struct object_entry *src_entry = src->entry;
@@ -1313,12 +1342,6 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	if (trg_entry->type != src_entry->type)
 		return -1;
 
-	/* We do not compute delta to *create* objects we are not
-	 * going to pack.
-	 */
-	if (trg_entry->preferred_base)
-		return -1;
-
 	/*
 	 * We do not bother to try a delta that we discarded
 	 * on an earlier try, but only when reusing delta data.
@@ -1355,24 +1378,28 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 
 	/* Load data if not already done */
 	if (!trg->data) {
+		read_lock();
 		trg->data = read_sha1_file(trg_entry->idx.sha1, &type, &sz);
+		read_unlock();
 		if (!trg->data)
 			die("object %s cannot be read",
 			    sha1_to_hex(trg_entry->idx.sha1));
 		if (sz != trg_size)
 			die("object %s inconsistent object length (%lu vs %lu)",
 			    sha1_to_hex(trg_entry->idx.sha1), sz, trg_size);
-		window_memory_usage += sz;
+		*mem_usage += sz;
 	}
 	if (!src->data) {
+		read_lock();
 		src->data = read_sha1_file(src_entry->idx.sha1, &type, &sz);
+		read_unlock();
 		if (!src->data)
 			die("object %s cannot be read",
 			    sha1_to_hex(src_entry->idx.sha1));
 		if (sz != src_size)
 			die("object %s inconsistent object length (%lu vs %lu)",
 			    sha1_to_hex(src_entry->idx.sha1), sz, src_size);
-		window_memory_usage += sz;
+		*mem_usage += sz;
 	}
 	if (!src->index) {
 		src->index = create_delta_index(src->data, src_size);
@@ -1382,7 +1409,7 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 				warning("suboptimal pack - out of memory");
 			return 0;
 		}
-		window_memory_usage += sizeof_delta_index(src->index);
+		*mem_usage += sizeof_delta_index(src->index);
 	}
 
 	delta_buf = create_delta(src->index, trg->data, trg_size, &delta_size, max_size);
@@ -1402,17 +1429,27 @@ static int try_delta(struct unpacked *trg, struct unpacked *src,
 	trg_entry->delta_size = delta_size;
 	trg->depth = src->depth + 1;
 
+	/*
+	 * Handle memory allocation outside of the cache
+	 * accounting lock.  Compiler will optimize the strangeness
+	 * away when THREADED_DELTA_SEARCH is not defined.
+	 */
+	if (trg_entry->delta_data)
+		free(trg_entry->delta_data);
+	cache_lock();
 	if (trg_entry->delta_data) {
 		delta_cache_size -= trg_entry->delta_size;
-		free(trg_entry->delta_data);
 		trg_entry->delta_data = NULL;
 	}
-
 	if (delta_cacheable(src_size, trg_size, delta_size)) {
-		trg_entry->delta_data = xrealloc(delta_buf, delta_size);
 		delta_cache_size += trg_entry->delta_size;
-	} else
+		cache_unlock();
+		trg_entry->delta_data = xrealloc(delta_buf, delta_size);
+	} else {
+		cache_unlock();
 		free(delta_buf);
+	}
+
 	return 1;
 }
 
@@ -1429,68 +1466,60 @@ static unsigned int check_delta_limit(struct object_entry *me, unsigned int n)
 	return m;
 }
 
-static void free_unpacked(struct unpacked *n)
+static unsigned long free_unpacked(struct unpacked *n)
 {
-	window_memory_usage -= sizeof_delta_index(n->index);
+	unsigned long freed_mem = sizeof_delta_index(n->index);
 	free_delta_index(n->index);
 	n->index = NULL;
 	if (n->data) {
+		freed_mem += n->entry->size;
 		free(n->data);
 		n->data = NULL;
-		window_memory_usage -= n->entry->size;
 	}
 	n->entry = NULL;
 	n->depth = 0;
+	return freed_mem;
 }
 
-static void find_deltas(struct object_entry **list, int window, int depth)
+static void find_deltas(struct object_entry **list, unsigned list_size,
+			int window, int depth, unsigned *processed)
 {
-	uint32_t i = nr_objects, idx = 0, count = 0, processed = 0;
+	uint32_t i = list_size, idx = 0, count = 0;
 	unsigned int array_size = window * sizeof(struct unpacked);
 	struct unpacked *array;
-	int max_depth;
+	unsigned long mem_usage = 0;
 
-	if (!nr_objects)
-		return;
 	array = xmalloc(array_size);
 	memset(array, 0, array_size);
-	if (progress)
-		start_progress(&progress_state, "Deltifying %u objects...", "", nr_result);
 
 	do {
 		struct object_entry *entry = list[--i];
 		struct unpacked *n = array + idx;
-		int j, best_base = -1;
-
-		if (!entry->preferred_base)
-			processed++;
+		int j, max_depth, best_base = -1;
 
-		if (progress)
-			display_progress(&progress_state, processed);
-
-		if (entry->delta)
-			/* This happens if we decided to reuse existing
-			 * delta from a pack.  "!no_reuse_delta &&" is implied.
-			 */
-			continue;
-
-		if (entry->size < 50)
-			continue;
-
-		if (entry->no_try_delta)
-			continue;
-
-		free_unpacked(n);
+		mem_usage -= free_unpacked(n);
 		n->entry = entry;
 
 		while (window_memory_limit &&
-		       window_memory_usage > window_memory_limit &&
+		       mem_usage > window_memory_limit &&
 		       count > 1) {
 			uint32_t tail = (idx + window - count) % window;
-			free_unpacked(array + tail);
+			mem_usage -= free_unpacked(array + tail);
 			count--;
 		}
 
+		/* We do not compute delta to *create* objects we are not
+		 * going to pack.
+		 */
+		if (entry->preferred_base)
+			goto next;
+
+		progress_lock();
+		(*processed)++;
+		if (progress)
+			display_progress(&progress_state, *processed);
+		progress_unlock();
+
 		/*
 		 * If the current object is at pack edge, take the depth the
 		 * objects that depend on the current object into account
@@ -1513,7 +1542,7 @@ static void find_deltas(struct object_entry **list, int window, int depth)
 			m = array + other_idx;
 			if (!m->entry)
 				break;
-			ret = try_delta(n, m, max_depth);
+			ret = try_delta(n, m, max_depth, &mem_usage);
 			if (ret < 0)
 				break;
 			else if (ret > 0)
@@ -1552,9 +1581,6 @@ static void find_deltas(struct object_entry **list, int window, int depth)
 			idx = 0;
 	} while (i > 0);
 
-	if (progress)
-		stop_progress(&progress_state);
-
 	for (i = 0; i < window; ++i) {
 		free_delta_index(array[i].index);
 		free(array[i].data);
@@ -1562,21 +1588,145 @@ static void find_deltas(struct object_entry **list, int window, int depth)
 	free(array);
 }
 
+#ifdef THREADED_DELTA_SEARCH
+
+struct thread_params {
+	pthread_t thread;
+	struct object_entry **list;
+	unsigned list_size;
+	int window;
+	int depth;
+	unsigned *processed;
+};
+
+static pthread_mutex_t data_request  = PTHREAD_MUTEX_INITIALIZER;
+static pthread_mutex_t data_ready    = PTHREAD_MUTEX_INITIALIZER;
+static pthread_mutex_t data_provider = PTHREAD_MUTEX_INITIALIZER;
+static struct thread_params *data_requester;
+
+static void *threaded_find_deltas(void *arg)
+{
+	struct thread_params *me = arg;
+
+	for (;;) {
+		pthread_mutex_lock(&data_request);
+		data_requester = me;
+		pthread_mutex_unlock(&data_provider);
+		pthread_mutex_lock(&data_ready);
+		pthread_mutex_unlock(&data_request);
+
+		if (!me->list_size)
+			return NULL;
+
+		find_deltas(me->list, me->list_size,
+			    me->window, me->depth, me->processed);
+	}
+}
+
+static void ll_find_deltas(struct object_entry **list, unsigned list_size,
+			   int window, int depth, unsigned *processed)
+{
+	struct thread_params *target, p[delta_search_threads];
+	int i, ret;
+	unsigned chunk_size;
+
+	if (delta_search_threads <= 1) {
+		find_deltas(list, list_size, window, depth, processed);
+		return;
+	}
+
+	pthread_mutex_lock(&data_provider);
+	pthread_mutex_lock(&data_ready);
+
+	for (i = 0; i < delta_search_threads; i++) {
+		p[i].window = window;
+		p[i].depth = depth;
+		p[i].processed = processed;
+		ret = pthread_create(&p[i].thread, NULL,
+				     threaded_find_deltas, &p[i]);
+		if (ret)
+			die("unable to create thread: %s", strerror(ret));
+	}
+
+	/* this should be auto-tuned somehow */
+	chunk_size = window * 1000;
+
+	do {
+		unsigned sublist_size = chunk_size;
+		if (sublist_size > list_size)
+			sublist_size = list_size;
+
+		/* try to split chunks on "path" boundaries */
+		while (sublist_size < list_size && list[sublist_size]->hash &&
+		       list[sublist_size]->hash == list[sublist_size-1]->hash)
+			sublist_size++;
+
+		pthread_mutex_lock(&data_provider);
+		target = data_requester;
+		target->list = list;
+		target->list_size = sublist_size;
+		pthread_mutex_unlock(&data_ready);
+
+		list += sublist_size;
+		list_size -= sublist_size;
+		if (!sublist_size) {
+			pthread_join(target->thread, NULL);
+			i--;
+		}
+	} while (i);
+}
+
+#else
+#define ll_find_deltas find_deltas
+#endif
+
 static void prepare_pack(int window, int depth)
 {
 	struct object_entry **delta_list;
-	uint32_t i;
+	uint32_t i, n, nr_deltas;
 
 	get_object_details();
 
-	if (!window || !depth)
+	if (!nr_objects || !window || !depth)
 		return;
 
 	delta_list = xmalloc(nr_objects * sizeof(*delta_list));
-	for (i = 0; i < nr_objects; i++)
-		delta_list[i] = objects + i;
-	qsort(delta_list, nr_objects, sizeof(*delta_list), type_size_sort);
-	find_deltas(delta_list, window+1, depth);
+	nr_deltas = n = 0;
+
+	for (i = 0; i < nr_objects; i++) {
+		struct object_entry *entry = objects + i;
+
+		if (entry->delta)
+			/* This happens if we decided to reuse existing
+			 * delta from a pack.  "!no_reuse_delta &&" is implied.
+			 */
+			continue;
+
+		if (entry->size < 50)
+			continue;
+
+		if (entry->no_try_delta)
+			continue;
+
+		if (!entry->preferred_base)
+			nr_deltas++;
+
+		delta_list[n++] = entry;
+	}
+
+	if (nr_deltas) {
+		unsigned nr_done = 0;
+		if (progress)
+			start_progress(&progress_state,
+				       "Deltifying %u objects...", "",
+				       nr_deltas);
+		qsort(delta_list, n, sizeof(*delta_list), type_size_sort);
+		ll_find_deltas(delta_list, n, window+1, depth, &nr_done);
+		if (progress)
+			stop_progress(&progress_state);
+		if (nr_done != nr_deltas)
+			die("inconsistency with delta count");
+	}
 	free(delta_list);
 }
 
@@ -1612,6 +1762,17 @@ static int git_pack_config(const char *k, const char *v)
 		cache_max_small_delta_size = git_config_int(k, v);
 		return 0;
 	}
+	if (!strcmp(k, "pack.threads")) {
+		delta_search_threads = git_config_int(k, v);
+		if (delta_search_threads < 1)
+			die("invalid number of threads specified (%d)",
+			    delta_search_threads);
+#ifndef THREADED_DELTA_SEARCH
+		if (delta_search_threads > 1)
+			warning("no threads support, ignoring %s", k);
+#endif
+		return 0;
+	}
 	return git_default_config(k, v);
 }
 
@@ -1771,6 +1932,18 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 				usage(pack_usage);
 			continue;
 		}
+		if (!prefixcmp(arg, "--threads=")) {
+			char *end;
+			delta_search_threads = strtoul(arg+10, &end, 0);
+			if (!arg[10] || *end || delta_search_threads < 1)
+				usage(pack_usage);
+#ifndef THREADED_DELTA_SEARCH
+			if (delta_search_threads > 1)
+				warning("no threads support, "
+					"ignoring %s", arg);
+#endif
+			continue;
+		}
 		if (!prefixcmp(arg, "--depth=")) {
 			char *end;
 			depth = strtoul(arg+8, &end, 0);