Hi,
On Mon, 15 Feb 2016 10:19:49 +0200
Sagi Grimberg <sagig@xxxxxxxxxxxxxxxxxx> wrote:
>
> > +/*
> > + * bio_get_last_bvec() is introduced to get the last bvec of one
> > + * bio for bio_will_gap().
> > + *
> > + * TODO: make it more efficient.
> > + */
> > +static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
> > +{
> > + struct bvec_iter iter;
> > +
> > + bio_for_each_segment(*bv, bio, iter)
> > + if (bv->bv_len == iter.bi_size)
> > + break;
> > +}
>
> This helper is used for each req/bio once or more. I'd say
No, the helper is only used for the non-splitted BIO, and all
splitted BIO is marked as non-merge.
> it's critical to make it efficient and not settle for
> a quick bail for drivers that don't have a virt_boundary
> like you did in patch #2.
Cc Kent and Keith.
Follows another version which should be more efficient.
Kent and Keith, I appreciate much if you may give a review on it.
diff --git a/include/linux/bio.h b/include/linux/bio.h
index 56d2db8..ef45fec 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -278,11 +278,21 @@ static inline void bio_get_first_bvec(struct bio *bio, struct bio_vec *bv)
*/
static inline void bio_get_last_bvec(struct bio *bio, struct bio_vec *bv)
{
- struct bvec_iter iter;
+ struct bvec_iter iter = bio->bi_iter;
+ int idx;
+
+ bio_advance_iter(bio, &iter, iter.bi_size);
+
+ WARN_ON(!iter.bi_idx && !iter.bi_bvec_done);
+
+ if (!iter.bi_bvec_done)
+ idx = iter.bi_idx - 1;
+ else /* in the middle of bvec */
+ idx = iter.bi_idx;
- bio_for_each_segment(*bv, bio, iter)
- if (bv->bv_len == iter.bi_size)
- break;
+ *bv = bio->bi_io_vec[idx];
+ if (iter.bi_bvec_done)
+ bv->bv_len = iter.bi_bvec_done;
}
/*
>
> However, given that it's a regression bug fix I'm not sure it's the best
> idea to add logic here.
But the issue is obviously in bio_will_gap(), isn't it?
Simply reverting 52cc6eead9095(block: blk-merge: fast-clone bio when splitting rw bios)
still might cause performance regression too.
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