On 04/05/2017 08:39, Fam Zheng wrote:
> On Thu, 04/20 14:00, Paolo Bonzini wrote:
>> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
>> ---
>> block/io.c | 3 ++-
>> block/nfs.c | 4 +++-
>> block/sheepdog.c | 3 ++-
>> include/block/block.h | 5 +++--
>> include/block/block_int.h | 4 ++--
>> 5 files changed, 12 insertions(+), 7 deletions(-)
>>
>> diff --git a/block/io.c b/block/io.c
>> index 869322a..3b2ede9 100644
>> --- a/block/io.c
>> +++ b/block/io.c
>> @@ -501,7 +501,8 @@ static void dummy_bh_cb(void *opaque)
>>
>> void bdrv_wakeup(BlockDriverState *bs)
>> {
>> - if (bs->wakeup) {
>> + /* The barrier (or an atomic op) is in the caller. */
>
> Why not add a barrier here so that callers don't need to worry about that?
Barriers are relatively expensive, and the common case is
dataplane7:block/io.c-void bdrv_dec_in_flight(BlockDriverState *bs)
dataplane7:block/io.c-{
dataplane7:block/io.c- atomic_dec(&bs->in_flight);
dataplane7:block/io.c: bdrv_wakeup(bs);
dataplane7:block/io.c-}
Paolo
>> + if (atomic_read(&bs->wakeup)) {
>> aio_bh_schedule_oneshot(qemu_get_aio_context(), dummy_bh_cb, NULL);
>> }
>> }
>
> Fam
>
