Re: [Qemu-devel] [PATCH] block: fix initialization in bdrv_io_limits_enable()

[Paolo Bonzini <pbonzini@redhat.com>]

Il 11/01/2013 13:29, Peter Lieven ha scritto:
> bdrv_io_limits_enable() starts a new slice, but does not set io_base
> correctly for that slice.
> 
> Here is how io_base is used:
> 
>    bytes_base  = bs->nr_bytes[is_write] - bs->io_base.bytes[is_write];
>    bytes_res   = (unsigned) nb_sectors * BDRV_SECTOR_SIZE;
> 
>    if (bytes_base + bytes_res <= bytes_limit) {
>        /* no wait */
>    } else {
>        /* operation needs to be throttled */
>    }
> 
> As a result, any I/O operations that are triggered between now and
> bs->slice_end are incorrectly limited.  If 10 MB of data has been
> written since the VM was started, QEMU thinks that 10 MB of data has
> been written in this slice. This leads to a I/O lockup in the guest.
> 
> We fix this by delaying the start of a new slice to the next
> call of bdrv_exceed_io_limits().
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
>  block.c |    4 ----
>  1 file changed, 4 deletions(-)
> 
> diff --git a/block.c b/block.c
> index 4e28c55..a40a389 100644
> --- a/block.c
> +++ b/block.c
> @@ -155,10 +155,6 @@ void bdrv_io_limits_enable(BlockDriverState *bs)
>  {
>      qemu_co_queue_init(&bs->throttled_reqs);
>      bs->block_timer = qemu_new_timer_ns(vm_clock, bdrv_block_timer, bs);
> -    bs->slice_time  = 5 * BLOCK_IO_SLICE_TIME;
> -    bs->slice_start = qemu_get_clock_ns(vm_clock);
> -    bs->slice_end   = bs->slice_start + bs->slice_time;
> -    memset(&bs->io_base, 0, sizeof(bs->io_base));
>      bs->io_limits_enabled = true;
>  }
> 

Thanks!

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

Paolo