[PATCH 2/4] migration: check for rate_limit_max for RATE_LIMIT_DISABLED

[Elena Ufimtseva <elena.ufimtseva@oracle.com>]

In migration rate limiting atomic operations are used
to read the rate limit variables and transferred bytes and
they are expensive. Check first if rate_limit_max is equal
to RATE_LIMIT_DISABLED and return false immediately if so.

Signed-off-by: Elena Ufimtseva <elena.ufimtseva@oracle.com>
---
 migration/migration-stats.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/migration/migration-stats.c b/migration/migration-stats.c
index 095d6d75bb..abc31483d5 100644
--- a/migration/migration-stats.c
+++ b/migration/migration-stats.c
@@ -24,14 +24,14 @@ bool migration_rate_exceeded(QEMUFile *f)
         return true;
     }
 
-    uint64_t rate_limit_start = stat64_get(&mig_stats.rate_limit_start);
-    uint64_t rate_limit_current = migration_transferred_bytes(f);
-    uint64_t rate_limit_used = rate_limit_current - rate_limit_start;
     uint64_t rate_limit_max = stat64_get(&mig_stats.rate_limit_max);
-
     if (rate_limit_max == RATE_LIMIT_DISABLED) {
         return false;
     }
+    uint64_t rate_limit_start = stat64_get(&mig_stats.rate_limit_start);
+    uint64_t rate_limit_current = migration_transferred_bytes(f);
+    uint64_t rate_limit_used = rate_limit_current - rate_limit_start;
+
     if (rate_limit_max > 0 && rate_limit_used > rate_limit_max) {
         return true;
     }
-- 
2.34.1