Merge branch 'np/auto-thread'

* np/auto-thread:
  Force t5302 to use a single thread
  pack-objects: don't use too many threads with few objects
  autodetect number of CPUs by default when using threads

builtin-pack-objects.c

@@ -78,7 +78,7 @@ static int progress = 1;
 static int window = 10;
 static uint32_t pack_size_limit, pack_size_limit_cfg;
 static int depth = 50;
-static int delta_search_threads = 1;
+static int delta_search_threads;
 static int pack_to_stdout;
 static int num_preferred_base;
 static struct progress *progress_state;
@@ -1612,11 +1612,18 @@ static void ll_find_deltas(struct object_entry **list, unsigned list_size,
 		find_deltas(list, &list_size, window, depth, processed);
 		return;
 	}
+	if (progress > pack_to_stdout)
+		fprintf(stderr, "Delta compression using %d threads.\n",
+				delta_search_threads);
 
 	/* Partition the work amongst work threads. */
 	for (i = 0; i < delta_search_threads; i++) {
 		unsigned sub_size = list_size / (delta_search_threads - i);
 
+		/* don't use too small segments or no deltas will be found */
+		if (sub_size < 2*window && i+1 < delta_search_threads)
+			sub_size = 0;
+
 		p[i].window = window;
 		p[i].depth = depth;
 		p[i].processed = processed;

t/t5302-pack-index.sh

@@ -10,6 +10,7 @@ test_expect_success \
     'setup' \
     'rm -rf .git
      git init &&
+     git config pack.threads 1 &&
      i=1 &&
      while test $i -le 100
      do