[PATCH v6 4/7] config: add new index.threads config setting

@@ -2413,6 +2413,13 @@ imap::
 	The configuration variables in the 'imap' section are described
 	in linkgit:git-imap-send[1].
 
+index.threads::
+	Specifies the number of threads to spawn when loading the index.
+	This is meant to reduce index load time on multiprocessor machines.
+	Specifying 0 or 'true' will cause Git to auto-detect the number of
+	CPU's and set the number of threads accordingly. Specifying 1 or
+	'false' will disable multithreading. Defaults to 'true'.
+
 index.version::
 	Specify the version with which new index files should be
 	initialized.  This does not affect existing repositories.

@@ -2289,6 +2289,24 @@ int git_config_get_fsmonitor(void)
 	return 0;
 }
 
+int git_config_get_index_threads(void)
+{
+	int is_bool, val = 0;
+
+	val = git_env_ulong("GIT_TEST_INDEX_THREADS", 0);
+	if (val)
+		return val;
+
+	if (!git_config_get_bool_or_int("index.threads", &is_bool, &val)) {
+		if (is_bool)
+			return val ? 0 : 1;
+		else
+			return val;
+	}
+
+	return 0; /* auto */
+}
+
 NORETURN
 void git_die_config_linenr(const char *key, const char *filename, int linenr)
 {

@@ -250,6 +250,7 @@ extern int git_config_get_untracked_cache(void);
 extern int git_config_get_split_index(void);
 extern int git_config_get_max_percent_split_change(void);
 extern int git_config_get_fsmonitor(void);
+extern int git_config_get_index_threads(void);
 
 /* This dies if the configured or default date is in the future */
 extern int git_config_get_expiry(const char *key, const char **output);

@@ -332,6 +332,11 @@ This is used to allow tests 1, 4-9 in t1700-split-index.sh to succeed
 as they currently hard code SHA values for the index which are no longer
 valid due to the addition of the EOIE extension.
 
+GIT_TEST_INDEX_THREADS=<n> enables exercising the multi-threaded loading
+of the index for the whole test suite by bypassing the default number of
+cache entries and thread minimums. Settting this to 1 will make the
+index loading single threaded.
+
 Naming Tests
 ------------
 

@@ -8,6 +8,7 @@ test_description='split index mode tests'
 sane_unset GIT_TEST_SPLIT_INDEX
 sane_unset GIT_FSMONITOR_TEST
 GIT_TEST_DISABLE_EOIE=true; export GIT_TEST_DISABLE_EOIE
+GIT_TEST_INDEX_THREADS=1; export GIT_TEST_INDEX_THREADS
 
 test_expect_success 'enable split index' '
 	git config splitIndex.maxPercentChange 100 &&