Commit 27ff42e2 authored by Michael Chapman's avatar Michael Chapman Committed by Juan Quintela
Browse files

migration: avoid divide by zero in xbzrle cache miss rate 



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: default avatarMichael Chapman <mike@very.puzzling.org>
Reviewed-by: default avatarAmit Shah <amit.shah@redhat.com>
Signed-off-by: default avatarJuan Quintela <quintela@redhat.com>
parent 50e9a629

arch_init.c

+5 −3
Original line number Diff line number Diff line
@@ -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 bytes_xfer_prev;

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)

{

    start_time = 0;

    bytes_xfer_prev = 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[] */
@@ -679,8 +683,6 @@ static void migration_bitmap_sync(void) 
    MigrationState *s = migrate_get_current();

    int64_t end_time;

    int64_t bytes_xfer_now;

    static uint64_t xbzrle_cache_miss_prev;

    static uint64_t iterations_prev;



    bitmap_sync_count++;
@@ -728,7 +730,7 @@ static void migration_bitmap_sync(void) 
             mig_throttle_on = false;

        }

        if (migrate_use_xbzrle()) {

            if (iterations_prev != 0) {

            if (iterations_prev != acct_info.iterations) {

                acct_info.xbzrle_cache_miss_rate =

                   (double)(acct_info.xbzrle_cache_miss -

                            xbzrle_cache_miss_prev) /