On Wed, Mar 24, 2021 at 04:32:31PM +0100, Hannes Reinecke wrote:
> On 3/24/21 1:19 PM, Ming Lei wrote:
> > Add one req flag REQ_POLL_CTX which will be used in the following patch for
> > supporting bio based IO polling.
> >
> > Exactly this flag can help us to do:
> >
> > 1) request flag is cloned in bio_fast_clone(), so if we mark one FS bio
> > as REQ_POLL_CTX, all bios cloned from this FS bio will be marked as
> > REQ_POLL_CTX too.
> >
> > 2) create per-task io polling context if the bio based queue supports
> > polling and the submitted bio is HIPRI. Per-task io poll context will be
> > created during submit_bio() before marking this HIPRI bio as REQ_POLL_CTX.
> > Then we can avoid to create such io polling context if one cloned bio with
> > REQ_POLL_CTX is submitted from another kernel context.
> >
> > 3) for supporting bio based io polling, we need to poll IOs from all
> > underlying queues of the bio device, this way help us to recognize which
> > IO needs to polled in bio based style, which will be applied in
> > following patch.
> >
> > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > ---
> > block/blk-core.c | 25 ++++++++++++++++++++++++-
> > include/linux/blk_types.h | 4 ++++
> > 2 files changed, 28 insertions(+), 1 deletion(-)
> >
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index 4671bbf31fd3..eb07d61cfdc2 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -840,11 +840,30 @@ static inline bool blk_queue_support_bio_poll(struct request_queue *q)
> > static inline void blk_bio_poll_preprocess(struct request_queue *q,
> > struct bio *bio)
> > {
> > + bool mq;
> > +
> > if (!(bio->bi_opf & REQ_HIPRI))
> > return;
> > - if (!blk_queue_poll(q) || (!queue_is_mq(q) && !blk_get_bio_poll_ctx()))
> > + /*
> > + * Can't support bio based IO polling without per-task poll ctx
> > + *
> > + * We have created per-task io poll context, and mark this
> > + * bio as REQ_POLL_CTX, so: 1) if any cloned bio from this bio is
> > + * submitted from another kernel context, we won't create bio
> > + * poll context for it, and that bio can be completed by IRQ;
> > + * 2) If such bio is submitted from current context, we will
> > + * complete it via blk_poll(); 3) If driver knows that one
> > + * underlying bio allocated from driver is for FS bio, meantime
> > + * it is submitted in current context, driver can mark such bio
> > + * as REQ_HIPRI & REQ_POLL_CTX manually, so the bio can be completed
> > + * via blk_poll too.
> > + */
> > + mq = queue_is_mq(q);
> > + if (!blk_queue_poll(q) || (!mq && !blk_get_bio_poll_ctx()))
> > bio->bi_opf &= ~REQ_HIPRI;
> > + else if (!mq)
> > + bio->bi_opf |= REQ_POLL_CTX;
> > }
> > static noinline_for_stack bool submit_bio_checks(struct bio *bio)
> > @@ -894,8 +913,12 @@ static noinline_for_stack bool submit_bio_checks(struct bio *bio)
> > /*
> > * Create per-task io poll ctx if bio polling supported and HIPRI
> > * set.
> > + *
> > + * If REQ_POLL_CTX isn't set for this HIPRI bio, we think it originated
> > + * from FS and allocate io polling context.
> > */
> > blk_create_io_context(q, blk_queue_support_bio_poll(q) &&
> > + !(bio->bi_opf & REQ_POLL_CTX) &&
> > (bio->bi_opf & REQ_HIPRI));
> > blk_bio_poll_preprocess(q, bio);
> > diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> > index db026b6ec15a..99160d588c2d 100644
> > --- a/include/linux/blk_types.h
> > +++ b/include/linux/blk_types.h
> > @@ -394,6 +394,9 @@ enum req_flag_bits {
> > __REQ_HIPRI,
> > + /* for marking IOs originated from same FS bio in same context */
> > + __REQ_POLL_CTX,
> > +
> > /* for driver use */
> > __REQ_DRV,
> > __REQ_SWAP, /* swapping request. */
> > @@ -418,6 +421,7 @@ enum req_flag_bits {
> > #define REQ_NOUNMAP (1ULL << __REQ_NOUNMAP)
> > #define REQ_HIPRI (1ULL << __REQ_HIPRI)
> > +#define REQ_POLL_CTX (1ULL << __REQ_POLL_CTX)
> > #define REQ_DRV (1ULL << __REQ_DRV)
> > #define REQ_SWAP (1ULL << __REQ_SWAP)
> >
> What happens to split bios?
> Will they be tracked similarly to cloned bios?
> If so, shouldn't you document that here, too?
split bios are simply cloned bios, please see bio_split().
thanks,
Ming
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