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 <[email protected]>
> >
> > ---
> > 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.
> and then submit next split bio, repeating the above process. I'm afraid
> the performance may be an issue here, since the batch every time
> blk_poll() reaps may decrease.
Could you benchmark it?
> Besides, the submitting routine and polling routine is bound together
> here, i.e., polling is always synchronous.
__split_and_process_bio calls __split_and_process_non_flush in a loop and
__split_and_process_non_flush records the poll cookie in ci.poll_cookie.
When we processed all the bios, we poll for the last cookie here:
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)) ;
}
Mikulas
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