Hi, Mikulas,
Mikulas Patocka <mpatocka@xxxxxxxxxx> writes:
> On Wed, 3 Mar 2021, JeffleXu wrote:
>
>>
>>
>> On 3/3/21 3:05 AM, Mikulas Patocka wrote:
>>
>> > Support I/O polling if submit_bio_noacct_mq_direct returned non-empty
>> > cookie.
>> >
>> > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>> >
>> > ---
>> > drivers/md/dm.c | 5 +++++
>> > 1 file changed, 5 insertions(+)
>> >
>> > Index: linux-2.6/drivers/md/dm.c
>> > ===================================================================
>> > --- linux-2.6.orig/drivers/md/dm.c 2021-03-02 19:26:34.000000000 +0100
>> > +++ linux-2.6/drivers/md/dm.c 2021-03-02 19:26:34.000000000 +0100
>> > @@ -1682,6 +1682,11 @@ static void __split_and_process_bio(stru
>> > }
>> > }
>> >
>> > + if (ci.poll_cookie != BLK_QC_T_NONE) {
>> > + while (atomic_read(&ci.io->io_count) > 1 &&
>> > + blk_poll(ci.poll_queue, ci.poll_cookie, true)) ;
>> > + }
>> > +
>> > /* drop the extra reference count */
>> > dec_pending(ci.io, errno_to_blk_status(error));
>> > }
>>
>> It seems that the general idea of your design is to
>> 1) submit *one* split bio
>> 2) blk_poll(), waiting the previously submitted split bio complets
>
> No, I submit all the bios and poll for the last one.
What happens if the last bio completes first? It looks like you will
call blk_poll with a cookie that already completed, and I'm pretty sure
that's invalid.
Thanks,
Jeff
