[PULL 06/20] migration/dirtyrate: move init step of calculation to main thread

[Juan Quintela <quintela@xxxxxxxxxx>]

From: Hyman Huang(黄勇) <huangy81@xxxxxxxxxxxxxxx>

since main thread may "query dirty rate" at any time, it's better
to move init step into main thead so that synchronization overhead
between "main" and "get_dirtyrate" can be reduced.

Signed-off-by: Hyman Huang(黄勇) <huangy81@xxxxxxxxxxxxxxx>
Message-Id: <109f8077518ed2f13068e3bfb10e625e964780f1.1624040308.git.huangy81@xxxxxxxxxxxxxxx>
Reviewed-by: Peter Xu <peterx@xxxxxxxxxx>
Reviewed-by: Juan Quintela <quintela@xxxxxxxxxx>
Signed-off-by: Juan Quintela <quintela@xxxxxxxxxx>
---
 migration/dirtyrate.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c
index a9bdd60034..b8f61cc650 100644
--- a/migration/dirtyrate.c
+++ b/migration/dirtyrate.c
@@ -380,7 +380,6 @@ void *get_dirtyrate_thread(void *arg)
 {
     struct DirtyRateConfig config = *(struct DirtyRateConfig *)arg;
     int ret;
-    int64_t start_time;
     rcu_register_thread();
 
     ret = dirtyrate_set_state(&CalculatingState, DIRTY_RATE_STATUS_UNSTARTED,
@@ -390,9 +389,6 @@ void *get_dirtyrate_thread(void *arg)
         return NULL;
     }
 
-    start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;
-    init_dirtyrate_stat(start_time, config);
-
     calculate_dirtyrate(config);
 
     ret = dirtyrate_set_state(&CalculatingState, DIRTY_RATE_STATUS_MEASURING,
@@ -411,6 +407,7 @@ void qmp_calc_dirty_rate(int64_t calc_time, bool has_sample_pages,
     static struct DirtyRateConfig config;
     QemuThread thread;
     int ret;
+    int64_t start_time;
 
     /*
      * If the dirty rate is already being measured, don't attempt to start.
@@ -451,6 +448,10 @@ void qmp_calc_dirty_rate(int64_t calc_time, bool has_sample_pages,
     config.sample_period_seconds = calc_time;
     config.sample_pages_per_gigabytes = sample_pages;
     config.mode = DIRTY_RATE_MEASURE_MODE_PAGE_SAMPLING;
+
+    start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;
+    init_dirtyrate_stat(start_time, config);
+
     qemu_thread_create(&thread, "get_dirtyrate", get_dirtyrate_thread,
                        (void *)&config, QEMU_THREAD_DETACHED);
 }
-- 
2.33.1