Re: [Qemu-devel] [RFC v2 21/33] migration: new cmd MIG_CMD_POSTCOPY_RESUME

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Peter Xu (peterx@redhat.com) wrote:
> Introducing this new command to be sent when the source VM is ready to
> resume the paused migration.  What the destination does here is
> basically release the fault thread to continue service page faults.
> 
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  migration/savevm.c     | 33 +++++++++++++++++++++++++++++++++
>  migration/savevm.h     |  1 +
>  migration/trace-events |  1 +
>  3 files changed, 35 insertions(+)
> 
> diff --git a/migration/savevm.c b/migration/savevm.c
> index 7f77a31..e914346 100644
> --- a/migration/savevm.c
> +++ b/migration/savevm.c
> @@ -77,6 +77,7 @@ enum qemu_vm_cmd {
>      MIG_CMD_POSTCOPY_RAM_DISCARD,  /* A list of pages to discard that
>                                        were previously sent during
>                                        precopy but are dirty. */
> +    MIG_CMD_POSTCOPY_RESUME,       /* resume postcopy on dest */
>      MIG_CMD_PACKAGED,          /* Send a wrapped stream within this stream */
>      MIG_CMD_RECV_BITMAP,       /* Request for recved bitmap on dst */
>      MIG_CMD_MAX
> @@ -95,6 +96,7 @@ static struct mig_cmd_args {
>      [MIG_CMD_POSTCOPY_RUN]     = { .len =  0, .name = "POSTCOPY_RUN" },
>      [MIG_CMD_POSTCOPY_RAM_DISCARD] = {
>                                     .len = -1, .name = "POSTCOPY_RAM_DISCARD" },
> +    [MIG_CMD_POSTCOPY_RESUME]  = { .len =  0, .name = "POSTCOPY_RESUME" },
>      [MIG_CMD_PACKAGED]         = { .len =  4, .name = "PACKAGED" },
>      [MIG_CMD_RECV_BITMAP]      = { .len = -1, .name = "RECV_BITMAP" },
>      [MIG_CMD_MAX]              = { .len = -1, .name = "MAX" },
> @@ -931,6 +933,12 @@ void qemu_savevm_send_postcopy_run(QEMUFile *f)
>      qemu_savevm_command_send(f, MIG_CMD_POSTCOPY_RUN, 0, NULL);
>  }
>  
> +void qemu_savevm_send_postcopy_resume(QEMUFile *f)
> +{
> +    trace_savevm_send_postcopy_resume();
> +    qemu_savevm_command_send(f, MIG_CMD_POSTCOPY_RESUME, 0, NULL);
> +}
> +
>  void qemu_savevm_send_recv_bitmap(QEMUFile *f, char *block_name)
>  {
>      size_t len;
> @@ -1682,6 +1690,28 @@ static int loadvm_postcopy_handle_run(MigrationIncomingState *mis)
>      return LOADVM_QUIT;
>  }
>  
> +static int loadvm_postcopy_handle_resume(MigrationIncomingState *mis)
> +{
> +    if (mis->state != MIGRATION_STATUS_POSTCOPY_RECOVER) {
> +        error_report("%s: illegal resume received", __func__);
> +        /* Don't fail the load, only for this. */
> +        return 0;
> +    }
> +
> +    /*
> +     * This means source VM is ready to resume the postcopy migration.
> +     * It's time to switch state and release the fault thread to
> +     * continue service page faults.
> +     */
> +    migrate_set_state(&mis->state, MIGRATION_STATUS_POSTCOPY_RECOVER,
> +                      MIGRATION_STATUS_POSTCOPY_ACTIVE);
> +    qemu_sem_post(&mis->postcopy_pause_sem_fault);
> +
> +    /* TODO: Tell source that "we are ready" */
> +

You might want to add a trace in here; however,


Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> +    return 0;
> +}
> +
>  /**
>   * Immediately following this command is a blob of data containing an embedded
>   * chunk of migration stream; read it and load it.
> @@ -1847,6 +1877,9 @@ static int loadvm_process_command(QEMUFile *f)
>      case MIG_CMD_POSTCOPY_RAM_DISCARD:
>          return loadvm_postcopy_ram_handle_discard(mis, len);
>  
> +    case MIG_CMD_POSTCOPY_RESUME:
> +        return loadvm_postcopy_handle_resume(mis);
> +
>      case MIG_CMD_RECV_BITMAP:
>          return loadvm_handle_recv_bitmap(mis, len);
>      }
> diff --git a/migration/savevm.h b/migration/savevm.h
> index 8126b1c..a5f3879 100644
> --- a/migration/savevm.h
> +++ b/migration/savevm.h
> @@ -46,6 +46,7 @@ int qemu_savevm_send_packaged(QEMUFile *f, const uint8_t *buf, size_t len);
>  void qemu_savevm_send_postcopy_advise(QEMUFile *f);
>  void qemu_savevm_send_postcopy_listen(QEMUFile *f);
>  void qemu_savevm_send_postcopy_run(QEMUFile *f);
> +void qemu_savevm_send_postcopy_resume(QEMUFile *f);
>  void qemu_savevm_send_recv_bitmap(QEMUFile *f, char *block_name);
>  
>  void qemu_savevm_send_postcopy_ram_discard(QEMUFile *f, const char *name,
> diff --git a/migration/trace-events b/migration/trace-events
> index 9960cd8..0a1c302 100644
> --- a/migration/trace-events
> +++ b/migration/trace-events
> @@ -35,6 +35,7 @@ savevm_send_open_return_path(void) ""
>  savevm_send_ping(uint32_t val) "0x%x"
>  savevm_send_postcopy_listen(void) ""
>  savevm_send_postcopy_run(void) ""
> +savevm_send_postcopy_resume(void) ""
>  savevm_send_recv_bitmap(char *name) "%s"
>  savevm_state_setup(void) ""
>  savevm_state_header(void) ""
> -- 
> 2.7.4
> 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK