[sheepdog] [PATCH v2] dog/farm: add an option for multi-thread cluster snapshot save process

[Liu Yuan]

There is no reason we can't multi-thread it. Let's go multi-threading and enjoy
boost.

Consider that we often save snapshots on the fly so we use single thread as
default to minimize the impact of running cluster.

usage:
 $ dog cluster snapshot save -m ... # enable multi-threads

Signed-off-by: Liu Yuan <namei.unix at gmail.com>
---
 dog/cluster.c   | 8 +++++++-
 dog/farm/farm.c | 5 +++--
 dog/farm/farm.h | 2 +-
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/dog/cluster.c b/dog/cluster.c
index e36e308..12dabac 100644
--- a/dog/cluster.c
+++ b/dog/cluster.c
@@ -21,6 +21,8 @@ static struct sd_option cluster_options[] = {
 	{'b', "store", true, "specify backend store"},
 	{'c', "copies", true, "specify the default data redundancy (number of copies)"},
 	{'f', "force", false, "do not prompt for confirmation"},
+	{'m', "multithread", false,
+	 "use multi-thread for 'cluster snapshot save'"},
 	{'t', "strict", false,
 	 "do not serve write request if number of nodes is not sufficient"},
 	{ 0, NULL, false, NULL },
@@ -29,6 +31,7 @@ static struct sd_option cluster_options[] = {
 static struct cluster_cmd_data {
 	uint8_t copies;
 	uint8_t copy_policy;
+	uint8_t multithread;
 	bool force;
 	bool strict;
 	char name[STORE_LEN];
@@ -432,7 +435,8 @@ static int save_snapshot(int argc, char **argv)
 		goto out;
 	}
 
-	if (farm_save_snapshot(tag) != SD_RES_SUCCESS)
+	if (farm_save_snapshot(tag, cluster_cmd_data.multithread)
+	    != SD_RES_SUCCESS)
 		goto out;
 
 	ret = EXIT_SUCCESS;
@@ -788,6 +792,8 @@ static int cluster_parser(int ch, const char *opt)
 	case 'f':
 		cluster_cmd_data.force = true;
 		break;
+	case 'm':
+		cluster_cmd_data.multithread = true;
 	case 't':
 		cluster_cmd_data.strict = true;
 		break;
diff --git a/dog/farm/farm.c b/dog/farm/farm.c
index e4f532e..5d07be9 100644
--- a/dog/farm/farm.c
+++ b/dog/farm/farm.c
@@ -315,7 +315,7 @@ static int queue_save_snapshot_work(uint64_t oid, uint32_t nr_copies,
 	return 0;
 }
 
-int farm_save_snapshot(const char *tag)
+int farm_save_snapshot(const char *tag, bool multithread)
 {
 	unsigned char trunk_sha1[SHA1_DIGEST_SIZE];
 	struct strbuf trunk_buf;
@@ -357,7 +357,8 @@ int farm_save_snapshot(const char *tag)
 
 	strbuf_init(&trunk_buf, sizeof(struct trunk_entry) * nr_objects);
 
-	wq = create_work_queue("save snapshot", WQ_ORDERED);
+	wq = create_work_queue("save snapshot",
+			       multithread ? WQ_DYNAMIC : WQ_ORDERED);
 	if (for_each_object_in_tree(queue_save_snapshot_work,
 				    &trunk_buf) < 0) {
 		ret = -1;
diff --git a/dog/farm/farm.h b/dog/farm/farm.h
index b95006a..745aa15 100644
--- a/dog/farm/farm.h
+++ b/dog/farm/farm.h
@@ -59,7 +59,7 @@ struct vdi_option {
 /* farm.c */
 int farm_init(const char *path);
 bool farm_contain_snapshot(uint32_t idx, const char *tag);
-int farm_save_snapshot(const char *tag);
+int farm_save_snapshot(const char *tag, bool);
 int farm_load_snapshot(uint32_t idx, const char *tag, int count, char **name);
 int farm_show_snapshot(uint32_t idx, const char *tag, int count, char **name);
 char *get_object_directory(void);
-- 
1.9.1