Re: [Qemu-devel] [PATCH] block/mirror: Sleep periodically during bitmap scanning

[Paolo Bonzini <pbonzini@redhat.com>]

On 13/05/2015 05:11, Fam Zheng wrote:
> Before, we only yield after initializing dirty bitmap, where the QMP
> command would return. That may take very long, and guest IO will be
> blocked.
> 
> Add sleep points like the later mirror iterations.

You were also planning to let bdrv_co_is_allocated/get_block_status
return a larger p_num than nb_sectors---which maybe could make
nb_sectors obsolete completely, I don't know.  But this is already an
improvement.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

Thanks,

Paolo

> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block/mirror.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 1a1d997..baed225 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -467,11 +467,23 @@ static void coroutine_fn mirror_run(void *opaque)
>      sectors_per_chunk = s->granularity >> BDRV_SECTOR_BITS;
>      mirror_free_init(s);
>  
> +    last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
>      if (!s->is_none_mode) {
>          /* First part, loop on the sectors and initialize the dirty bitmap.  */
>          BlockDriverState *base = s->base;
>          for (sector_num = 0; sector_num < end; ) {
>              int64_t next = (sector_num | (sectors_per_chunk - 1)) + 1;
> +            int64_t now = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
> +
> +            if (now - last_pause_ns > SLICE_TIME) {
> +                last_pause_ns = now;
> +                block_job_sleep_ns(&s->common, QEMU_CLOCK_REALTIME, 0);
> +            }
> +
> +            if (block_job_is_cancelled(&s->common)) {
> +                goto immediate_exit;
> +            }
> +
>              ret = bdrv_is_allocated_above(bs, base,
>                                            sector_num, next - sector_num, &n);
>  
> @@ -490,7 +502,6 @@ static void coroutine_fn mirror_run(void *opaque)
>      }
>  
>      bdrv_dirty_iter_init(s->dirty_bitmap, &s->hbi);
> -    last_pause_ns = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
>      for (;;) {
>          uint64_t delay_ns = 0;
>          int64_t cnt;
>