fetch: add top-level trace2 regions

At $DAYJOB we experienced some slow fetch operations and needed some
additional data to help diagnose the issue.

Add top-level trace2 regions for the various modes of operation of
`git-fetch`. None of these regions are in recursive code, so any
enclosed trace messages should only see their nesting level increase by
one.

Signed-off-by: Josh Steadmon <steadmon@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/fetch.c

@@ -2408,6 +2408,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 		struct oidset_iter iter;
 		const struct object_id *oid;
 
+		trace2_region_enter("fetch", "negotiate-only", the_repository);
 		if (!remote)
 			die(_("must supply remote when using --negotiate-only"));
 		gtransport = prepare_transport(remote, 1);
@@ -2416,6 +2417,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 		} else {
 			warning(_("protocol does not support --negotiate-only, exiting"));
 			result = 1;
+			trace2_region_leave("fetch", "negotiate-only", the_repository);
 			goto cleanup;
 		}
 		if (server_options.nr)
@@ -2426,11 +2428,17 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 		while ((oid = oidset_iter_next(&iter)))
 			printf("%s\n", oid_to_hex(oid));
 		oidset_clear(&acked_commits);
+		trace2_region_leave("fetch", "negotiate-only", the_repository);
 	} else if (remote) {
-		if (filter_options.choice || repo_has_promisor_remote(the_repository))
+		if (filter_options.choice || repo_has_promisor_remote(the_repository)) {
+			trace2_region_enter("fetch", "setup-partial", the_repository);
 			fetch_one_setup_partial(remote);
+			trace2_region_leave("fetch", "setup-partial", the_repository);
+		}
+		trace2_region_enter("fetch", "fetch-one", the_repository);
 		result = fetch_one(remote, argc, argv, prune_tags_ok, stdin_refspecs,
 				   &config);
+		trace2_region_leave("fetch", "fetch-one", the_repository);
 	} else {
 		int max_children = max_jobs;
 
@@ -2450,7 +2458,9 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 			max_children = config.parallel;
 
 		/* TODO should this also die if we have a previous partial-clone? */
+		trace2_region_enter("fetch", "fetch-multiple", the_repository);
 		result = fetch_multiple(&list, max_children, &config);
+		trace2_region_leave("fetch", "fetch-multiple", the_repository);
 	}
 
 	/*
@@ -2472,6 +2482,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 			max_children = config.parallel;
 
 		add_options_to_argv(&options, &config);
+		trace2_region_enter_printf("fetch", "recurse-submodule", the_repository, "%s", submodule_prefix);
 		result = fetch_submodules(the_repository,
 					  &options,
 					  submodule_prefix,
@@ -2479,6 +2490,7 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 					  recurse_submodules_default,
 					  verbosity < 0,
 					  max_children);
+		trace2_region_leave_printf("fetch", "recurse-submodule", the_repository, "%s", submodule_prefix);
 		strvec_clear(&options);
 	}
 
@@ -2502,9 +2514,11 @@ int cmd_fetch(int argc, const char **argv, const char *prefix)
 		if (progress)
 			commit_graph_flags |= COMMIT_GRAPH_WRITE_PROGRESS;
 
+		trace2_region_enter("fetch", "write-commit-graph", the_repository);
 		write_commit_graph_reachable(the_repository->objects->odb,
 					     commit_graph_flags,
 					     NULL);
+		trace2_region_leave("fetch", "write-commit-graph", the_repository);
 	}
 
 	if (enable_auto_gc) {

bundle-uri.c

@@ -13,6 +13,7 @@
 #include "config.h"
 #include "fetch-pack.h"
 #include "remote.h"
+#include "trace2.h"
 
 static struct {
 	enum bundle_list_heuristic heuristic;
@@ -799,6 +800,8 @@ int fetch_bundle_uri(struct repository *r, const char *uri,
 		.id = xstrdup(""),
 	};
 
+	trace2_region_enter("fetch", "fetch-bundle-uri", the_repository);
+
 	init_bundle_list(&list);
 
 	/*
@@ -824,6 +827,7 @@ cleanup:
 	for_all_bundles_in_list(&list, unlink_bundle, NULL);
 	clear_bundle_list(&list);
 	clear_remote_bundle_info(&bundle, NULL);
+	trace2_region_leave("fetch", "fetch-bundle-uri", the_repository);
 	return result;
 }