Users may need to check the xbzrle encoding rate to know if the guest
memory is xbzrle encoding-friendly, and dynamically turn off the
encoding if the encoding rate is low.
Signed-off-by: Yi Sun <yi.y....@intel.com>
Signed-off-by: Wei Wang <wei.w.w...@intel.com>
---
migration/migration.c | 1 +
migration/ram.c | 39 +++++++++++++++++++++++++++++++++++++--
monitor/hmp-cmds.c | 2 ++
qapi/migration.json | 5 ++++-
4 files changed, 44 insertions(+), 3 deletions(-)
diff --git a/migration/migration.c b/migration/migration.c
index 187ac0410c..e40421353c 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -930,6 +930,7 @@ static void populate_ram_info(MigrationInfo *info,
MigrationState *s)
info->xbzrle_cache->pages = xbzrle_counters.pages;
info->xbzrle_cache->cache_miss = xbzrle_counters.cache_miss;
info->xbzrle_cache->cache_miss_rate = xbzrle_counters.cache_miss_rate;
+ info->xbzrle_cache->encoding_rate = xbzrle_counters.encoding_rate;
info->xbzrle_cache->overflow = xbzrle_counters.overflow;
}
diff --git a/migration/ram.c b/migration/ram.c
index 04f13feb2e..41b75a0a0f 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -327,6 +327,10 @@ struct RAMState {
uint64_t num_dirty_pages_period;
/* xbzrle misses since the beginning of the period */
uint64_t xbzrle_cache_miss_prev;
+ /* Amount of xbzrle pages since the beginning of the period */
+ uint64_t xbzrle_pages_prev;
+ /* Amount of xbzrle encoded bytes since the beginning of the period */
+ uint64_t xbzrle_bytes_prev;
/* compression statistics since the beginning of the period */
/* amount of count that no free thread to compress data */
@@ -696,6 +700,18 @@ static int save_xbzrle_page(RAMState *rs, uint8_t
**current_data,
return -1;
}
+ /*
+ * Reaching here means the page has hit the xbzrle cache, no matter what
+ * encoding result it is (normal encoding, overflow or skipping the page),
+ * count the page as encoded. This is used to caculate the encoding rate.
+ *
+ * Example: 2 pages (8KB) being encoded, first page encoding generates 2KB,
+ * 2nd page turns out to be skipped (i.e. no new bytes written to the
+ * page), the overall encoding rate will be 8KB / 2KB = 4, which has the
+ * skipped page included. In this way, the encoding rate can tell if the
+ * guest page is good for xbzrle encoding.
+ */
+ xbzrle_counters.pages++;
prev_cached_page = get_cached_data(XBZRLE.cache, current_addr);
/* save current buffer into memory */
@@ -726,6 +742,7 @@ static int save_xbzrle_page(RAMState *rs, uint8_t
**current_data,
} else if (encoded_len == -1) {
trace_save_xbzrle_page_overflow();
xbzrle_counters.overflow++;
+ xbzrle_counters.bytes += TARGET_PAGE_SIZE;
return -1;
}
@@ -736,8 +753,12 @@ static int save_xbzrle_page(RAMState *rs, uint8_t
**current_data,
qemu_put_be16(rs->f, encoded_len);
qemu_put_buffer(rs->f, XBZRLE.encoded_buf, encoded_len);
bytes_xbzrle += encoded_len + 1 + 2;
- xbzrle_counters.pages++;
- xbzrle_counters.bytes += bytes_xbzrle;
+ /*
+ * Like compressed_size (please see update_compress_thread_counts),
+ * the xbzrle encoded bytes don't count the 8 byte header with
+ * RAM_SAVE_FLAG_CONTINUE.
+ */
+ xbzrle_counters.bytes += bytes_xbzrle - 8;
ram_counters.transferred += bytes_xbzrle;
return 1;
@@ -870,9 +891,23 @@ static void migration_update_rates(RAMState *rs, int64_t
end_time)
}
if (migrate_use_xbzrle()) {
+ double encoded_size, unencoded_size;
+
xbzrle_counters.cache_miss_rate = (double)(xbzrle_counters.cache_miss -
rs->xbzrle_cache_miss_prev) / page_count;
rs->xbzrle_cache_miss_prev = xbzrle_counters.cache_miss;
+ unencoded_size = (xbzrle_counters.pages - rs->xbzrle_pages_prev) *
+ TARGET_PAGE_SIZE;
+ encoded_size = xbzrle_counters.bytes - rs->xbzrle_bytes_prev;
+ if (xbzrle_counters.pages == rs->xbzrle_pages_prev) {
+ xbzrle_counters.encoding_rate = 0;
+ } else if (!encoded_size) {
+ xbzrle_counters.encoding_rate = UINT64_MAX;
+ } else {
+ xbzrle_counters.encoding_rate = unencoded_size / encoded_size;
+ }
+ rs->xbzrle_pages_prev = xbzrle_counters.pages;
+ rs->xbzrle_bytes_prev = xbzrle_counters.bytes;
}
if (migrate_use_compression()) {
diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
index 9b94e67879..c2a3a667ae 100644
--- a/monitor/hmp-cmds.c
+++ b/monitor/hmp-cmds.c
@@ -303,6 +303,8 @@ void hmp_info_migrate(Monitor *mon, const QDict *qdict)
info->xbzrle_cache->cache_miss);
monitor_printf(mon, "xbzrle cache miss rate: %0.2f\n",
info->xbzrle_cache->cache_miss_rate);
+ monitor_printf(mon, "xbzrle encoding rate: %0.2f\n",
+ info->xbzrle_cache->encoding_rate);
monitor_printf(mon, "xbzrle overflow: %" PRIu64 "\n",
info->xbzrle_cache->overflow);
}
diff --git a/qapi/migration.json b/qapi/migration.json
index eca2981d0a..358e40226d 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -70,6 +70,8 @@
#
# @cache-miss-rate: rate of cache miss (since 2.1)
#
+# @encoding-rate: rate of encoded bytes (since 5.1)
+#
# @overflow: number of overflows
#
# Since: 1.2
@@ -77,7 +79,7 @@
{ 'struct': 'XBZRLECacheStats',
'data': {'cache-size': 'int', 'bytes': 'int', 'pages': 'int',
'cache-miss': 'int', 'cache-miss-rate': 'number',
- 'overflow': 'int' } }
+ 'encoding-rate': 'number', 'overflow': 'int' } }
##
# @CompressionStats:
@@ -337,6 +339,7 @@
# "pages":2444343,
# "cache-miss":2244,
# "cache-miss-rate":0.123,
+# "encoding-rate":80.1,
# "overflow":34434
# }
# }
--
2.20.1
