Re: [Qemu-devel] [PATCH 03/21] backup: improve non-dirty bits progress processing

[Fam Zheng <famz@redhat.com>]

On Fri, 12/23 17:28, Vladimir Sementsov-Ogievskiy wrote:
> Set fake progress for non-dirty clusters in copy_bitmap initialization,
> to:
> 1. set progress in the same place where corresponding clusters are
> consumed from copy_bitmap (or not initialized, as here)
> 2. earlier progress information for user
> 3. simplify the code
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>  block/backup.c | 18 +++---------------
>  1 file changed, 3 insertions(+), 15 deletions(-)
> 
> diff --git a/block/backup.c b/block/backup.c
> index 621b1c0..f1f87f6 100644
> --- a/block/backup.c
> +++ b/block/backup.c
> @@ -383,7 +383,6 @@ static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
>      int64_t sector;
>      int64_t cluster;
>      int64_t end;
> -    int64_t last_cluster = -1;
>      int64_t sectors_per_cluster = cluster_size_sectors(job);
>      BdrvDirtyBitmapIter *dbi;
>  
> @@ -395,12 +394,6 @@ static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
>      while ((sector = bdrv_dirty_iter_next(dbi)) != -1) {
>          cluster = sector / sectors_per_cluster;
>  
> -        /* Fake progress updates for any clusters we skipped */
> -        if (cluster != last_cluster + 1) {
> -            job->common.offset += ((cluster - last_cluster - 1) *
> -                                   job->cluster_size);
> -        }
> -
>          for (end = cluster + clusters_per_iter; cluster < end; cluster++) {
>              do {
>                  if (yield_and_check(job)) {
> @@ -422,14 +415,6 @@ static int coroutine_fn backup_run_incremental(BackupBlockJob *job)
>          if (granularity < job->cluster_size) {
>              bdrv_set_dirty_iter(dbi, cluster * sectors_per_cluster);
>          }
> -
> -        last_cluster = cluster - 1;
> -    }
> -
> -    /* Play some final catchup with the progress meter */
> -    end = DIV_ROUND_UP(job->common.len, job->cluster_size);
> -    if (last_cluster + 1 < end) {
> -        job->common.offset += ((end - last_cluster - 1) * job->cluster_size);
>      }
>  
>  out:
> @@ -462,6 +447,9 @@ static void backup_incremental_init_copy_bitmap(BackupBlockJob *job)
>          bdrv_set_dirty_iter(dbi, (cluster + cl_gran) * sectors_per_cluster);
>      }
>  
> +    job->common.offset = job->common.len -
> +                         hbitmap_count(job->copy_bitmap) * job->cluster_size;
> +
>      bdrv_dirty_iter_free(dbi);
>  }

Is this effectively moving the progress reporting from cluster copying to dirty
bitmap initialization? If so the progress will stay "100%" once
backup_incremental_init_copy_bitmap returns, but the backup has merely started.
I don't think this is a good idea.

Fam