Commit 4abc7855 authored by Ivan Ren's avatar Ivan Ren Committed by zhuyanting
Browse files

migration: always initialise ram_counters for a new migration 



This patch fix a multifd migration bug in migration speed calculation, this
problem can be reproduced as follows:
1. start a vm and give a heavy memory write stress to prevent the vm be
   successfully migrated to destination
2. begin a migration with multifd
3. migrate for a long time [actually, this can be measured by transferred bytes]
4. migrate cancel
5. begin a new migration with multifd, the migration will directly run into
   migration_completion phase

Reason as follows:

Migration update bandwidth and s->threshold_size in function
migration_update_counters after BUFFER_DELAY time:

    current_bytes = migration_total_bytes(s);
    transferred = current_bytes - s->iteration_initial_bytes;
    time_spent = current_time - s->iteration_start_time;
    bandwidth = (double)transferred / time_spent;
    s->threshold_size = bandwidth * s->parameters.downtime_limit;

In multifd migration, migration_total_bytes function return
qemu_ftell(s->to_dst_file) + ram_counters.multifd_bytes.
s->iteration_initial_bytes will be initialized to 0 at every new migration,
but ram_counters is a global variable, and history migration data will be
accumulated. So if the ram_counters.multifd_bytes is big enough, it may lead
pending_size >= s->threshold_size become false in migration_iteration_run
after the first migration_update_counters.

Change-Id: Ib153d8676a5b82650bfb1156060e09f0d29f3ac6
Signed-off-by: default avatarIvan Ren <ivanren@tencent.com>
Reviewed-by: default avatarJuan Quintela <quintela@redhat.com>
Reviewed-by: default avatarWei Yang <richardw.yang@linux.intel.com>
Suggested-by: default avatarWei Yang <richardw.yang@linux.intel.com>
Message-Id: <1564741121-1840-1-git-send-email-ivanren@tencent.com>
Signed-off-by: default avatarDr. David Alan Gilbert <dgilbert@redhat.com>
parent 17781f15

migration/migration.c

+19 −6
Original line number Diff line number Diff line
@@ -1908,6 +1908,11 @@ static bool migrate_prepare(MigrationState *s, bool blk, bool blk_inc, 
    }



    migrate_init(s);

    /*

     * set ram_counters memory to zero for a

     * new migration

     */

    memset(&ram_counters, 0, sizeof(ram_counters));



    return true;

}
@@ -3025,6 +3030,17 @@ static void migration_calculate_complete(MigrationState *s) 
    }

}



static void update_iteration_initial_status(MigrationState *s)

{

    /*

     * Update these three fields at the same time to avoid mismatch info lead

     * wrong speed calculation.

     */

    s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);

    s->iteration_initial_bytes = migration_total_bytes(s);

    s->iteration_initial_pages = ram_get_total_transferred_pages();

}



static void migration_update_counters(MigrationState *s,

                                      int64_t current_time)

{
@@ -3060,9 +3076,7 @@ static void migration_update_counters(MigrationState *s, 


    qemu_file_reset_rate_limit(s->to_dst_file);



    s->iteration_start_time = current_time;

    s->iteration_initial_bytes = current_bytes;

    s->iteration_initial_pages = ram_get_total_transferred_pages();

    update_iteration_initial_status(s);



    trace_migrate_transferred(transferred, time_spent,

                              bandwidth, s->threshold_size);
@@ -3186,7 +3200,7 @@ static void *migration_thread(void *opaque) 
    rcu_register_thread();



    object_ref(OBJECT(s));

    s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);

    update_iteration_initial_status(s);



    qemu_savevm_state_header(s->to_dst_file);
@@ -3251,8 +3265,7 @@ static void *migration_thread(void *opaque) 
             * the local variables. This is important to avoid

             * breaking transferred_bytes and bandwidth calculation

             */

            s->iteration_start_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);

            s->iteration_initial_bytes = 0;

            update_iteration_initial_status(s);

        }



        current_time = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);

migration/savevm.c

+1 −0
Original line number Diff line number Diff line
@@ -1424,6 +1424,7 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp) 
    }



    migrate_init(ms);

    memset(&ram_counters, 0, sizeof(ram_counters));

    ms->to_dst_file = f;



    qemu_mutex_unlock_iothread();