Re: [Qemu-devel] [PATCH v1 1/3] block: block: introduce bdrv_io_plug() and bdrv_io_unplug()

[Ming Lei <ming.lei@canonical.com>]

On Tue, Jul 1, 2014 at 12:10 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> Il 30/06/2014 17:47, Ming Lei ha scritto:
>
>> From: Ming Lei <tom.leiming@gmail.com>
>>
>> This patch introduces these two APIs so that following
>> patches can support queuing I/O requests and submitting them
>> at batch for improving I/O performance.
>>
>> Signed-off-by: Ming Lei <ming.lei@canonical.com>
>> ---
>>  block.c                   |   22 ++++++++++++++++++++++
>>  include/block/block.h     |    3 +++
>>  include/block/block_int.h |    4 ++++
>>  3 files changed, 29 insertions(+)
>>
>> diff --git a/block.c b/block.c
>> index 217f523..2b4ec5b 100644
>> --- a/block.c
>> +++ b/block.c
>> @@ -1910,6 +1910,7 @@ void bdrv_drain_all(void)
>>              bool bs_busy;
>>
>>              aio_context_acquire(aio_context);
>> +            bdrv_io_unplug(bs);
>>              bdrv_start_throttled_reqs(bs);
>>              bs_busy = bdrv_requests_pending(bs);
>>              bs_busy |= aio_poll(aio_context, bs_busy);
>> @@ -5774,3 +5775,24 @@ bool bdrv_is_first_non_filter(BlockDriverState
>> *candidate)
>>
>>      return false;
>>  }
>> +
>> +void bdrv_io_plug(BlockDriverState *bs)
>> +{
>> +    BlockDriver *drv = bs->drv;
>> +    if (drv && drv->bdrv_io_plug) {
>> +        drv->bdrv_io_plug(bs);
>> +    } else if (bs->file) {
>> +        bdrv_io_plug(bs->file);
>> +    }
>> +}
>> +
>> +int bdrv_io_unplug(BlockDriverState *bs)
>> +{
>> +    BlockDriver *drv = bs->drv;
>> +    if (drv && drv->bdrv_io_unplug) {
>> +        return drv->bdrv_io_unplug(bs);
>> +    } else if (bs->file) {
>> +        return bdrv_io_unplug(bs->file);
>> +    }
>> +    return 0;
>
>
> I think this should return void (and that's how you use it in patch 3
> indeed).  If you fix this you can add my Reviewed-by tag.

It can be used to trace how many IO are submitted at batch,
otherwise device can't know this information at all.

Thanks,
--
Ming Lei