[Qemu-devel] [PATCH 1/2] migration: introduce compress-wait-thread-adaptive

[guangrong . xiao]

From: Xiao Guangrong <address@hidden>

Currently we have two behaviors if all threads are busy to do compression,
the main thread mush wait one of them becoming free if @compress-wait-thread
set to on or the main thread can directly return without wait and post
the page out as normal one

Both of them have its profits and short-comes, however, if the bandwidth is
not limited extremely so that compression can not use out all of it bandwidth,
at the same time, the migration process is easily throttled if we posted too
may pages as normal pages. None of them can work properly under this case

In order to use the bandwidth more effectively, we introduce the third
behavior, compress-wait-thread-adaptive, which make the main thread wait
if there is no bandwidth left or let the page go out as normal page if there
has enough bandwidth to make sure the migration process will not be
throttled

Signed-off-by: Xiao Guangrong <address@hidden>
---
 hmp.c                 |  11 +++++
 migration/migration.c |  37 ++++++++++++++++
 migration/migration.h |   4 ++
 migration/ram.c       | 118 +++++++++++++++++++++++++++++++++++++++++++++-----
 qapi/migration.json   |  26 ++++++++++-
 5 files changed, 184 insertions(+), 12 deletions(-)

diff --git a/hmp.c b/hmp.c
index 43ae9ec61a..2c5bb504d4 100644
--- a/hmp.c
+++ b/hmp.c
@@ -282,6 +282,8 @@ void hmp_info_migrate(Monitor *mon, const QDict *qdict)
                        info->compression->compressed_size);
         monitor_printf(mon, "compression rate: %0.2f\n",
                        info->compression->compression_rate);
+        monitor_printf(mon, "compress-no-wait-weight: %"PRIu64"\n",
+                       info->compression->compress_no_wait_weight);
     }
 
     if (info->has_cpu_throttle_percentage) {
@@ -344,6 +346,11 @@ void hmp_info_migrate_parameters(Monitor *mon, const QDict 
*qdict)
         monitor_printf(mon, "%s: %s\n",
             MigrationParameter_str(MIGRATION_PARAMETER_COMPRESS_WAIT_THREAD),
             params->compress_wait_thread ? "on" : "off");
+        assert(params->has_compress_wait_thread_adaptive);
+        monitor_printf(mon, "%s: %s\n",
+            MigrationParameter_str(
+                MIGRATION_PARAMETER_COMPRESS_WAIT_THREAD_ADAPTIVE),
+            params->compress_wait_thread_adaptive ? "on" : "off");
         assert(params->has_decompress_threads);
         monitor_printf(mon, "%s: %u\n",
             MigrationParameter_str(MIGRATION_PARAMETER_DECOMPRESS_THREADS),
@@ -1676,6 +1683,10 @@ void hmp_migrate_set_parameter(Monitor *mon, const QDict 
*qdict)
         p->has_compress_wait_thread = true;
         visit_type_bool(v, param, &p->compress_wait_thread, &err);
         break;
+    case MIGRATION_PARAMETER_COMPRESS_WAIT_THREAD_ADAPTIVE:
+        p->has_compress_wait_thread_adaptive = true;
+        visit_type_bool(v, param, &p->compress_wait_thread_adaptive, &err);
+        break;
     case MIGRATION_PARAMETER_DECOMPRESS_THREADS:
         p->has_decompress_threads = true;
         visit_type_int(v, param, &p->decompress_threads, &err);
diff --git a/migration/migration.c b/migration/migration.c
index 49ffb9997a..d19935b529 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -706,6 +706,9 @@ MigrationParameters *qmp_query_migrate_parameters(Error 
**errp)
     params->compress_threads = s->parameters.compress_threads;
     params->has_compress_wait_thread = true;
     params->compress_wait_thread = s->parameters.compress_wait_thread;
+    params->has_compress_wait_thread_adaptive = true;
+    params->compress_wait_thread_adaptive =
+                            s->parameters.compress_wait_thread_adaptive;
     params->has_decompress_threads = true;
     params->decompress_threads = s->parameters.decompress_threads;
     params->has_cpu_throttle_initial = true;
@@ -799,6 +802,8 @@ static void populate_ram_info(MigrationInfo *info, 
MigrationState *s)
                                     compression_counters.compressed_size;
         info->compression->compression_rate =
                                     compression_counters.compression_rate;
+        info->compression->compress_no_wait_weight =
+                                compression_counters.compress_no_wait_weight;
     }
 
     if (cpu_throttle_active()) {
@@ -1132,6 +1137,11 @@ static void 
migrate_params_test_apply(MigrateSetParameters *params,
         dest->compress_wait_thread = params->compress_wait_thread;
     }
 
+    if (params->has_compress_wait_thread_adaptive) {
+        dest->compress_wait_thread_adaptive =
+            params->compress_wait_thread_adaptive;
+    }
+
     if (params->has_decompress_threads) {
         dest->decompress_threads = params->decompress_threads;
     }
@@ -1204,6 +1214,11 @@ static void migrate_params_apply(MigrateSetParameters 
*params, Error **errp)
         s->parameters.compress_wait_thread = params->compress_wait_thread;
     }
 
+    if (params->has_compress_wait_thread_adaptive) {
+        s->parameters.compress_wait_thread_adaptive =
+            params->compress_wait_thread_adaptive;
+    }
+
     if (params->has_decompress_threads) {
         s->parameters.decompress_threads = params->decompress_threads;
     }
@@ -1925,6 +1940,15 @@ bool migrate_postcopy_blocktime(void)
     return s->enabled_capabilities[MIGRATION_CAPABILITY_POSTCOPY_BLOCKTIME];
 }
 
+int64_t migration_max_bandwidth(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.max_bandwidth;
+}
+
 bool migrate_use_compression(void)
 {
     MigrationState *s;
@@ -1961,6 +1985,15 @@ int migrate_compress_wait_thread(void)
     return s->parameters.compress_wait_thread;
 }
 
+int migrate_compress_wait_thread_adaptive(void)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    return s->parameters.compress_wait_thread_adaptive;
+}
+
 int migrate_decompress_threads(void)
 {
     MigrationState *s;
@@ -2898,6 +2931,8 @@ static void migration_update_counters(MigrationState *s,
     s->mbps = (((double) transferred * 8.0) /
                ((double) time_spent / 1000.0)) / 1000.0 / 1000.0;
 
+    compress_adaptive_update(s->mbps);
+
     /*
      * if we haven't sent anything, we don't want to
      * recalculate. 10000 is a small enough number for our purposes
@@ -3232,6 +3267,8 @@ static Property migration_properties[] = {
                       DEFAULT_MIGRATE_COMPRESS_THREAD_COUNT),
     DEFINE_PROP_BOOL("x-compress-wait-thread", MigrationState,
                       parameters.compress_wait_thread, true),
+    DEFINE_PROP_BOOL("x-ccompress-wait-thread-adaptive", MigrationState,
+                      parameters.compress_wait_thread_adaptive, false),
     DEFINE_PROP_UINT8("x-decompress-threads", MigrationState,
                       parameters.decompress_threads,
                       DEFAULT_MIGRATE_DECOMPRESS_THREAD_COUNT),
diff --git a/migration/migration.h b/migration/migration.h
index e413d4d8b6..d631776230 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -270,11 +270,15 @@ bool migrate_use_block(void);
 bool migrate_use_block_incremental(void);
 int migrate_max_cpu_throttle(void);
 bool migrate_use_return_path(void);
+int64_t migration_max_bandwidth(void);
 
 bool migrate_use_compression(void);
 int migrate_compress_level(void);
 int migrate_compress_threads(void);
 int migrate_compress_wait_thread(void);
+int migrate_compress_wait_thread_adaptive(void);
+void compress_adaptive_update(double mbps);
+
 int migrate_decompress_threads(void);
 bool migrate_use_events(void);
 bool migrate_postcopy_blocktime(void);
diff --git a/migration/ram.c b/migration/ram.c
index 7e7deec4d8..3b08a605e4 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -276,6 +276,8 @@ struct RAMSrcPageRequest {
     QSIMPLEQ_ENTRY(RAMSrcPageRequest) next_req;
 };
 
+#define COMPRESS_BUSY_COUNT_PERIOD 100
+
 /* State of RAM for migration */
 struct RAMState {
     /* QEMUFile used for this migration */
@@ -292,6 +294,19 @@ struct RAMState {
     bool ram_bulk_stage;
     /* How many times we have dirty too many pages */
     int dirty_rate_high_cnt;
+
+    /* used by by compress-wait-thread-adaptive */
+    /*
+     * the count for the case that all compress threads are busy to
+     * handle a page in a period
+     */
+    uint8_t compress_busy_count;
+    /*
+     * the number of pages that can be directly posted as normal page when
+     * all compress threads are busy in a period
+     */
+    uint8_t compress_no_wait_left;
+
     /* these variables are used for bitmap sync */
     /* last time we did a full bitmap_sync */
     int64_t time_last_bitmap_sync;
@@ -470,6 +485,8 @@ static void compress_threads_save_cleanup(void)
     comp_param = NULL;
 }
 
+static void compress_adaptive_init(void);
+
 static int compress_threads_save_setup(void)
 {
     int i, thread_count;
@@ -477,6 +494,9 @@ static int compress_threads_save_setup(void)
     if (!migrate_use_compression()) {
         return 0;
     }
+
+    compress_adaptive_init();
+
     thread_count = migrate_compress_threads();
     compress_threads = g_new0(QemuThread, thread_count);
     comp_param = g_new0(CompressParam, thread_count);
@@ -1593,6 +1613,67 @@ uint64_t ram_pagesize_summary(void)
     return summary;
 }
 
+static void compress_adaptive_init(void)
+{
+    /* fully wait on default. */
+     compression_counters.compress_no_wait_weight = 0;
+     ram_state->compress_no_wait_left = 0;
+     ram_state->compress_busy_count = 0;
+}
+
+void compress_adaptive_update(double mbps)
+{
+    int64_t rate_limit, remain_bw, max_bw = migration_max_bandwidth();
+
+    if (!migrate_use_compression() ||
+        !migrate_compress_wait_thread_adaptive()) {
+        return;
+    }
+
+    /* no bandwith is set to the file then we can not do adaptive adjustment */
+    rate_limit = qemu_file_get_rate_limit(migrate_get_current()->to_dst_file);
+    if (rate_limit == 0 || rate_limit == INT64_MAX) {
+        return;
+    }
+
+    max_bw = (max_bw >> 20) * 8;
+    remain_bw = abs(max_bw - (int64_t)(mbps));
+    if (remain_bw <= ((max_bw / 10) * 2)) {
+        /* if we have used all the bandwidth, let's compress more. */
+        if (compression_counters.compress_no_wait_weight) {
+            compression_counters.compress_no_wait_weight--;
+        }
+        goto exit;
+    }
+
+    /* have enough bandwidth left, do not need to compress so aggressively */
+    if (compression_counters.compress_no_wait_weight !=
+        COMPRESS_BUSY_COUNT_PERIOD) {
+        compression_counters.compress_no_wait_weight++;
+    }
+
+exit:
+    ram_state->compress_busy_count = 0;
+    ram_state->compress_no_wait_left =
+                            compression_counters.compress_no_wait_weight;
+}
+
+static bool compress_adaptive_need_wait(void)
+{
+    if (++ram_state->compress_busy_count == COMPRESS_BUSY_COUNT_PERIOD) {
+        ram_state->compress_busy_count = 0;
+        ram_state->compress_no_wait_left =
+                    compression_counters.compress_no_wait_weight;
+    }
+
+    if (ram_state->compress_no_wait_left) {
+        ram_state->compress_no_wait_left--;
+        return false;
+    }
+
+    return true;
+}
+
 static void migration_update_rates(RAMState *rs, int64_t end_time)
 {
     uint64_t page_count = rs->target_page_count - rs->target_page_count_prev;
@@ -1970,6 +2051,15 @@ static int compress_page_with_multi_thread(RAMState *rs, 
RAMBlock *block,
 {
     int idx, thread_count, bytes_xmit = -1, pages = -1;
     bool wait = migrate_compress_wait_thread();
+    bool adaptive = migrate_compress_wait_thread_adaptive();
+
+    /*
+     * 'compress-wait-thread-adaptive' has higher priority than
+     * 'compress-wait-thread'.
+     */
+    if (adaptive) {
+        wait = false;
+    }
 
     thread_count = migrate_compress_threads();
     qemu_mutex_lock(&comp_done_lock);
@@ -1984,20 +2074,29 @@ retry:
             qemu_mutex_unlock(&comp_param[idx].mutex);
             pages = 1;
             update_compress_thread_counts(&comp_param[idx], bytes_xmit);
-            break;
+            goto exit;
         }
     }
 
+    if (adaptive && !wait) {
+        /* it is the first time go to the loop */
+        wait = compress_adaptive_need_wait();
+    }
+
     /*
-     * wait for the free thread if the user specifies 'compress-wait-thread',
-     * otherwise we will post the page out in the main thread as normal page.
+     * wait for the free thread if the user specifies
+     * 'compress-wait-thread-adaptive' that detected the bandwidth is
+     * not enough or compress-wait-thread', otherwise we will post the
+     * page out in the main thread as normal page.
      */
-    if (pages < 0 && wait) {
+    if (wait) {
         qemu_cond_wait(&comp_done_cond, &comp_done_lock);
         goto retry;
     }
-    qemu_mutex_unlock(&comp_done_lock);
 
+
+exit:
+    qemu_mutex_unlock(&comp_done_lock);
     return pages;
 }
 
@@ -3147,19 +3246,18 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     RAMState **rsp = opaque;
     RAMBlock *block;
 
-    if (compress_threads_save_setup()) {
-        return -1;
-    }
-
     /* migration has already setup the bitmap, reuse it. */
     if (!migration_in_colo_state()) {
         if (ram_init_all(rsp) != 0) {
-            compress_threads_save_cleanup();
             return -1;
         }
     }
     (*rsp)->f = f;
 
+    if (compress_threads_save_setup()) {
+        return -1;
+    }
+
     rcu_read_lock();
 
     qemu_put_be64(f, ram_bytes_total() | RAM_SAVE_FLAG_MEM_SIZE);
diff --git a/qapi/migration.json b/qapi/migration.json
index 38d4c41d88..6d925c73fc 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -90,11 +90,16 @@
 #
 # @compression-rate: rate of compressed size
 #
+# @compress-no-wait-weight: it controls how many pages are directly posted
+#     out as normal page when all compression threads are currently busy.
+#     Only available if compress-wait-thread-adaptive is on. (Since 3.2)
+#
 # Since: 3.1
 ##
 { 'struct': 'CompressionStats',
   'data': {'pages': 'int', 'busy': 'int', 'busy-rate': 'number',
-          'compressed-size': 'int', 'compression-rate': 'number' } }
+          'compressed-size': 'int', 'compression-rate': 'number',
+          'compress-no-wait-weight': 'int'} }
 
 ##
 # @MigrationStatus:
@@ -490,6 +495,11 @@
 #                        compression thread to become available; otherwise,
 #                        send the page uncompressed. (Since 3.1)
 #
+# @compress-wait-thread-adaptive: Adaptively controls compress-wait-thread
+#          based on the rate limit and it's off on default. When it is on
+#          and it has enough bandwidth, it acts as compress-wait-thread is
+#          off. (Since 3.2)
+#
 # @decompress-threads: Set decompression thread count to be used in live
 #          migration, the decompression thread count is an integer between 1
 #          and 255. Usually, decompression is at least 4 times as fast as
@@ -558,7 +568,7 @@
 ##
 { 'enum': 'MigrationParameter',
   'data': ['compress-level', 'compress-threads', 'decompress-threads',
-           'compress-wait-thread',
+           'compress-wait-thread', 'compress-wait-thread-adaptive',
            'cpu-throttle-initial', 'cpu-throttle-increment',
            'tls-creds', 'tls-hostname', 'max-bandwidth',
            'downtime-limit', 'x-checkpoint-delay', 'block-incremental',
@@ -578,6 +588,11 @@
 #                        compression thread to become available; otherwise,
 #                        send the page uncompressed. (Since 3.1)
 #
+# @compress-wait-thread-adaptive: Adaptively controls compress-wait-thread
+#          based on the rate limit and it's off on default. When it is on
+#          and it has enough bandwidth, it acts as compress-wait-thread is
+#          off. (Since 3.2)
+#
 # @decompress-threads: decompression thread count
 #
 # @cpu-throttle-initial: Initial percentage of time guest cpus are
@@ -653,6 +668,7 @@
   'data': { '*compress-level': 'int',
             '*compress-threads': 'int',
             '*compress-wait-thread': 'bool',
+            '*compress-wait-thread-adaptive': 'bool',
             '*decompress-threads': 'int',
             '*cpu-throttle-initial': 'int',
             '*cpu-throttle-increment': 'int',
@@ -698,6 +714,11 @@
 #                        compression thread to become available; otherwise,
 #                        send the page uncompressed. (Since 3.1)
 #
+# @compress-wait-thread-adaptive: Adaptively controls compress-wait-thread
+#          based on the rate limit and it's off on default. When it is on
+#          and it has enough bandwidth, it acts as compress-wait-thread is
+#          off. (Since 3.2)
+#
 # @decompress-threads: decompression thread count
 #
 # @cpu-throttle-initial: Initial percentage of time guest cpus are
@@ -769,6 +790,7 @@
   'data': { '*compress-level': 'uint8',
             '*compress-threads': 'uint8',
             '*compress-wait-thread': 'bool',
+            '*compress-wait-thread-adaptive': 'bool',
             '*decompress-threads': 'uint8',
             '*cpu-throttle-initial': 'uint8',
             '*cpu-throttle-increment': 'uint8',
-- 
2.14.5