Re: [Qemu-devel] [PATCH 03/16] block: introduce bdrv_no_throttling_begin/end

[Paolo Bonzini <pbonzini@redhat.com>]

On 09/03/2016 02:45, Fam Zheng wrote:
>> > @@ -555,11 +574,7 @@ static int bdrv_prwv_co(BlockDriverState *bs, int64_t offset,
>> >       * will not fire; so the I/O throttling function has to be disabled here
>> >       * if it has been enabled.
>> >       */
>> > -    if (bs->io_limits_enabled) {
>> > -        fprintf(stderr, "Disabling I/O throttling on '%s' due "
>> > -                        "to synchronous I/O.\n", bdrv_get_device_name(bs));
>> > -        bdrv_io_limits_disable(bs);
>> > -    }
>> > +    bdrv_no_throttling_begin(bs);
>> >  
>> >      if (qemu_in_coroutine()) {
>> >          /* Fast-path if already in coroutine context */
>> > @@ -573,6 +588,8 @@ static int bdrv_prwv_co(BlockDriverState *bs, int64_t offset,
>> >              aio_poll(aio_context, true);
>> >          }
>> >      }
>> > +
>> > +    bdrv_no_throttling_end(bs);
> 
> Does this change the behavior? There wasn't a bdrv_io_limits_enable() here, and
> the throttle doesn't come back automatically. Just want to make sure it's
> intended.

Yes, it's intended.  As long as the I/O stays synchronous, throttling is
disabled.  If it starts to be asynchronous, it will be re-enabled
automatically.

Paolo