On 3/19/21 12:48 AM, Ming Lei wrote:
> Add one req flag REQ_TAG 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_TAG, all bios cloned from this FS bio will be marked as REQ_TAG.
>
> 2)create per-task io polling context if the bio based queue supports polling
> and the submitted bio is HIPRI. This per-task io polling context will be
> created during submit_bio() before marking this HIPRI bio as REQ_TAG. Then
> we can avoid to create such io polling context if one cloned bio with REQ_TAG
> is submitted from another kernel context.
>
> 3) for supporting bio based io polling, we need to poll IOs from all
> underlying queues of bio device/driver, this way help us to recognize which
> IOs need to polled in bio based style, which will be implemented in next
> patch.
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-core.c | 29 +++++++++++++++++++++++++++--
> include/linux/blk_types.h | 4 ++++
> 2 files changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 0b00c21cbefb..efc7a61a84b4 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 poll without per-task poll queue
> + *
> + * Now we have created per-task io poll context, and mark this
> + * bio as REQ_TAG, so: 1) if any cloned bio from this bio is
> + * submitted from another kernel context, we won't create bio
> + * poll context for it, so that bio will 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_TAG manually, so the bio can be completed via blk_poll
> + * too.
> + */
Sorry I can't understand case 3, could you please further explain it? If
'driver marks such bio as REQ_TAG manually', then per-task io poll
context won't be created, and thus REQ_HIPRI will be cleared, in which
case the bio will be completed by IRQ. How could it be completed by
blk_poll()?
> + mq = queue_is_mq(q);
> + if (!blk_queue_poll(q) || (!mq && !blk_get_bio_poll_ctx()))
> bio->bi_opf &= ~REQ_HIPRI;
If the use cases are mixed, saying one kernel context may submit IO with
and without REQ_TAG at the meantime (though I don't know if this
situation exists), then the above code may not work as we expect.
For example, dm-XXX will return DM_MAPIO_SUBMITTED and actually submits
the cloned bio (with REQ_TAG) with internal kernel threads. Besides,
dm-XXX will also allocate bio (without REQ_TAG) of itself for metadata
logging or something. When submitting bios (without REQ_TAG), per-task
io poll context will be allocated. Later when submitting cloned bios
(with REQ_TAG), the poll context already exists and thus REQ_HIPRI is
kept for these bios and they are submitted to polling hw queues.
> + else if (!mq)
> + bio->bi_opf |= REQ_TAG;
> }
>
> static noinline_for_stack bool submit_bio_checks(struct bio *bio)
> @@ -893,9 +912,15 @@ static noinline_for_stack bool submit_bio_checks(struct bio *bio)
>
> /*
> * Created per-task io poll queue if we supports bio polling
> - * and it is one HIPRI bio.
> + * and it is one HIPRI bio, and this HIPRI bio has to be from
> + * FS. If REQ_TAG isn't set for HIPRI bio, we think it originated
> + * from FS.
> + *
> + * Driver may allocated bio by itself and REQ_TAG is set, but they
> + * won't be marked as HIPRI.
> */
> blk_create_io_context(q, blk_queue_support_bio_poll(q) &&
> + !(bio->bi_opf & REQ_TAG) &&
> (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..a1bcade4bcc3 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_TAG,
> +
> /* 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_TAG (1ULL << __REQ_TAG)
>
> #define REQ_DRV (1ULL << __REQ_DRV)
> #define REQ_SWAP (1ULL << __REQ_SWAP)
>
--
Thanks,
Jeffle
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