migration/dirtyrate: make sample page count configurable

introduce optional sample-pages argument in calc-dirty-rate,
making sample page count per GB configurable so that more
accurate dirtyrate can be calculated.

Signed-off-by: Hyman Huang(黄勇) <huangy81@chinatelecom.cn>
Message-Id: <3103453a3b2796f929269c99a6ad81a9a7f1f405.1623027729.git.huangy81@chinatelecom.cn>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  Wrapped a couple of long lines

migration/dirtyrate.c

@@ -48,6 +48,12 @@ static bool is_sample_period_valid(int64_t sec)
     return true;
 }
 
+static bool is_sample_pages_valid(int64_t pages)
+{
+    return pages >= MIN_SAMPLE_PAGE_COUNT &&
+           pages <= MAX_SAMPLE_PAGE_COUNT;
+}
+
 static int dirtyrate_set_state(int *state, int old_state, int new_state)
 {
     assert(new_state < DIRTY_RATE_STATUS__MAX);
@@ -72,13 +78,15 @@ static struct DirtyRateInfo *query_dirty_rate_info(void)
     info->status = CalculatingState;
     info->start_time = DirtyStat.start_time;
     info->calc_time = DirtyStat.calc_time;
+    info->sample_pages = DirtyStat.sample_pages;
 
     trace_query_dirty_rate_info(DirtyRateStatus_str(CalculatingState));
 
     return info;
 }
 
-static void init_dirtyrate_stat(int64_t start_time, int64_t calc_time)
+static void init_dirtyrate_stat(int64_t start_time, int64_t calc_time,
+                                uint64_t sample_pages)
 {
     DirtyStat.total_dirty_samples = 0;
     DirtyStat.total_sample_count = 0;
@@ -86,6 +94,7 @@ static void init_dirtyrate_stat(int64_t start_time, int64_t calc_time)
     DirtyStat.dirty_rate = -1;
     DirtyStat.start_time = start_time;
     DirtyStat.calc_time = calc_time;
+    DirtyStat.sample_pages = sample_pages;
 }
 
 static void update_dirtyrate_stat(struct RamblockDirtyInfo *info)
@@ -361,6 +370,7 @@ void *get_dirtyrate_thread(void *arg)
     int ret;
     int64_t start_time;
     int64_t calc_time;
+    uint64_t sample_pages;
 
     ret = dirtyrate_set_state(&CalculatingState, DIRTY_RATE_STATUS_UNSTARTED,
                               DIRTY_RATE_STATUS_MEASURING);
@@ -371,7 +381,8 @@ void *get_dirtyrate_thread(void *arg)
 
     start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) / 1000;
     calc_time = config.sample_period_seconds;
-    init_dirtyrate_stat(start_time, calc_time);
+    sample_pages = config.sample_pages_per_gigabytes;
+    init_dirtyrate_stat(start_time, calc_time, sample_pages);
 
     calculate_dirtyrate(config);
 
@@ -383,7 +394,8 @@ void *get_dirtyrate_thread(void *arg)
     return NULL;
 }
 
-void qmp_calc_dirty_rate(int64_t calc_time, Error **errp)
+void qmp_calc_dirty_rate(int64_t calc_time, bool has_sample_pages,
+                         int64_t sample_pages, Error **errp)
 {
     static struct DirtyRateConfig config;
     QemuThread thread;
@@ -404,6 +416,17 @@ void qmp_calc_dirty_rate(int64_t calc_time, Error **errp)
         return;
     }
 
+    if (has_sample_pages) {
+        if (!is_sample_pages_valid(sample_pages)) {
+            error_setg(errp, "sample-pages is out of range[%d, %d].",
+                            MIN_SAMPLE_PAGE_COUNT,
+                            MAX_SAMPLE_PAGE_COUNT);
+            return;
+        }
+    } else {
+        sample_pages = DIRTYRATE_DEFAULT_SAMPLE_PAGES;
+    }
+
     /*
      * Init calculation state as unstarted.
      */
@@ -415,7 +438,7 @@ void qmp_calc_dirty_rate(int64_t calc_time, Error **errp)
     }
 
     config.sample_period_seconds = calc_time;
-    config.sample_pages_per_gigabytes = DIRTYRATE_DEFAULT_SAMPLE_PAGES;
+    config.sample_pages_per_gigabytes = sample_pages;
     qemu_thread_create(&thread, "get_dirtyrate", get_dirtyrate_thread,
                        (void *)&config, QEMU_THREAD_DETACHED);
 }

migration/dirtyrate.h

@@ -15,7 +15,6 @@
 
 /*
  * Sample 512 pages per GB as default.
- * TODO: Make it configurable.
  */
 #define DIRTYRATE_DEFAULT_SAMPLE_PAGES            512
 
@@ -35,6 +34,12 @@
 #define MIN_FETCH_DIRTYRATE_TIME_SEC              1
 #define MAX_FETCH_DIRTYRATE_TIME_SEC              60
 
+/*
+ * Take 1/16 pages in 1G as the maxmum sample page count
+ */
+#define MIN_SAMPLE_PAGE_COUNT                     128
+#define MAX_SAMPLE_PAGE_COUNT                     16384
+
 struct DirtyRateConfig {
     uint64_t sample_pages_per_gigabytes; /* sample pages per GB */
     int64_t sample_period_seconds; /* time duration between two sampling */
@@ -63,6 +68,7 @@ struct DirtyRateStat {
     int64_t dirty_rate; /* dirty rate in MB/s */
     int64_t start_time; /* calculation start time in units of second */
     int64_t calc_time; /* time duration of two sampling in units of second */
+    uint64_t sample_pages; /* sample pages per GB */
 };
 
 void *get_dirtyrate_thread(void *arg);

qapi/migration.json

@@ -1740,6 +1740,9 @@
 #
 # @calc-time: time in units of second for sample dirty pages
 #
+# @sample-pages: page count per GB for sample dirty pages
+#                the default value is 512 (since 6.1)
+#
 # Since: 5.2
 #
 ##
@@ -1747,7 +1750,8 @@
   'data': {'*dirty-rate': 'int64',
            'status': 'DirtyRateStatus',
            'start-time': 'int64',
-           'calc-time': 'int64'} }
+           'calc-time': 'int64',
+           'sample-pages': 'uint64'} }
 
 ##
 # @calc-dirty-rate:
@@ -1756,13 +1760,18 @@
 #
 # @calc-time: time in units of second for sample dirty pages
 #
+# @sample-pages: page count per GB for sample dirty pages
+#                the default value is 512 (since 6.1)
+#
 # Since: 5.2
 #
 # Example:
-#   {"command": "calc-dirty-rate", "data": {"calc-time": 1} }
+#   {"command": "calc-dirty-rate", "data": {"calc-time": 1,
+#                                           'sample-pages': 512} }
 #
 ##
-{ 'command': 'calc-dirty-rate', 'data': {'calc-time': 'int64'} }
+{ 'command': 'calc-dirty-rate', 'data': {'calc-time': 'int64',
+                                         '*sample-pages': 'int'} }
 
 ##
 # @query-dirty-rate: