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migration: avoid divide by zero in xbzrle cache miss rate

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This bug manifested itself as a VM that could not be resumed by libvirt
following a migration:

  # virsh resume example
  error: Failed to resume domain example
  error: internal error: cannot parse json {"return":
    {"xbzrle-cache":
      {..., "cache-miss-rate": -nan, ...},
      ...
    }
  }: lexical error: malformed number, a digit is required after the minus sign.

This patch also ensures xbzrle_cache_miss_prev and iterations_prev are
cleared at the start of the migration.

Signed-off-by: Michael Chapman <mike@very.puzzling.org>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Michael Chapman 2015-04-15 13:59:14 +10:00 committed by Juan Quintela
parent 50e9a629c6
commit 27ff42e29a
1 changed files with 5 additions and 3 deletions
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8
arch_init.c
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@ -663,12 +663,16 @@ static void migration_bitmap_sync_range(ram_addr_t start, ram_addr_t length)
static int64_t start_time; static int64_t start_time;
static int64_t bytes_xfer_prev; static int64_t bytes_xfer_prev;
static int64_t num_dirty_pages_period; static int64_t num_dirty_pages_period;
static uint64_t xbzrle_cache_miss_prev;
static uint64_t iterations_prev;
static void migration_bitmap_sync_init(void) static void migration_bitmap_sync_init(void)
{ {
start_time = 0; start_time = 0;
bytes_xfer_prev = 0; bytes_xfer_prev = 0;
num_dirty_pages_period = 0; num_dirty_pages_period = 0;
xbzrle_cache_miss_prev = 0;
iterations_prev = 0;
} }
/* Called with iothread lock held, to protect ram_list.dirty_memory[] */ /* Called with iothread lock held, to protect ram_list.dirty_memory[] */
@ -679,8 +683,6 @@ static void migration_bitmap_sync(void)
MigrationState *s = migrate_get_current(); MigrationState *s = migrate_get_current();
int64_t end_time; int64_t end_time;
int64_t bytes_xfer_now; int64_t bytes_xfer_now;
static uint64_t xbzrle_cache_miss_prev;
static uint64_t iterations_prev;
bitmap_sync_count++; bitmap_sync_count++;
@ -728,7 +730,7 @@ static void migration_bitmap_sync(void)
mig_throttle_on = false; mig_throttle_on = false;
} }
if (migrate_use_xbzrle()) { if (migrate_use_xbzrle()) {
if (iterations_prev != 0) { if (iterations_prev != acct_info.iterations) {
acct_info.xbzrle_cache_miss_rate = acct_info.xbzrle_cache_miss_rate =
(double)(acct_info.xbzrle_cache_miss - (double)(acct_info.xbzrle_cache_miss -
xbzrle_cache_miss_prev) / xbzrle_cache_miss_prev) /