optimise bvec/bio iteration

PATCH Applied Pavel Begunkov 3 participants 9 messages Nov 24, 2020 – Dec 2, 2020 Block layer

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Pavel Begunkov

author

2020-11-24 18:01 UTC #0 lore raw

cover optimise bvec/bio iteration

This adds simpler versions of bvec_iter_advance() and bio_advance_iter() (i.e. *_single()), that are faster but work with the restriction that @bytes shouldn't be more than available in the current bvec segment.

That covers most of bvec/bio iteration/foreach, that are massively inlined, and thus also nicely shrinks binary.

Others non core-block users might be updated on case by case basis (if applicable) after the change is merged.

Pavel Begunkov (2):
block: optimise for_each_bvec() advance
bio: optimise bvec iteration

 block/bio.c          |  4 ++--
 include/linux/bio.h  | 17 +++++++++++++++--
 include/linux/bvec.h | 20 +++++++++++++++-----
 3 files changed, 32 insertions(+), 9 deletions(-)

Signature · 1 line

2.24.0

Pavel Begunkov

author

2020-11-24 18:01 UTC #1 lore raw

PATCH 1/2 block: optimise for_each_bvec() advance

Because of how for_each_bvec() works it never advances across multiple entries at a time, so bvec_iter_advance() is an overkill. Add specialised bvec_iter_advance_single() that is faster. It also handles zero-len bvecs, so can kill bvec_iter_skip_zero_bvec().

text data bss dec hex filename
before:
23977 805 0 24782 60ce lib/iov_iter.o
before, bvec_iter_advance() w/o WARN_ONCE()
22886 600 0 23486 5bbe ./lib/iov_iter.o
after:
21862 600 0 22462 57be lib/iov_iter.o

Reviewed-by Ming Lei <[email protected]>

Signed-off-by Pavel Begunkov <[email protected]>

---
 include/linux/bvec.h | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

include/linux/bvec.h +15 -5

index 2efec10bf792..ff832e698efb 100644
@@ -121,18 +121,28 @@ static inline bool bvec_iter_advance(const struct bio_vec *bv,
 	return true;
 }
 
-static inline void bvec_iter_skip_zero_bvec(struct bvec_iter *iter)
+/*
+ * A simpler version of bvec_iter_advance(), @bytes should not span
+ * across multiple bvec entries, i.e. bytes <= bv[i->bi_idx].bv_len
+ */
+static inline void bvec_iter_advance_single(const struct bio_vec *bv,
+				struct bvec_iter *iter, unsigned int bytes)
 {
-	iter->bi_bvec_done = 0;
-	iter->bi_idx++;
+	unsigned int done = iter->bi_bvec_done + bytes;
+
+	if (done == bv[iter->bi_idx].bv_len) {
+		done = 0;
+		iter->bi_idx++;
+	}
+	iter->bi_bvec_done = done;
+	iter->bi_size -= bytes;
 }
 
 #define for_each_bvec(bvl, bio_vec, iter, start)			\
 	for (iter = (start);						\
 	     (iter).bi_size &&						\
 		((bvl = bvec_iter_bvec((bio_vec), (iter))), 1);	\
-	     (bvl).bv_len ? (void)bvec_iter_advance((bio_vec), &(iter),	\
-		     (bvl).bv_len) : bvec_iter_skip_zero_bvec(&(iter)))
+	     bvec_iter_advance_single((bio_vec), &(iter), (bvl).bv_len))
 
 /* for iterating one bio from start to end */
 #define BVEC_ITER_ALL_INIT (struct bvec_iter)				\

Signature · 1 line

2.24.0

Christoph Hellwig

Reviewed-by on v1 1/2

2020-11-26 10:01 UTC #2 lore raw

Re: [PATCH 1/2] block: optimise for_each_bvec() advance

Quoted 13 lines · Pavel Begunkov

Because of how for_each_bvec() works it never advances across multiple entries at a time, so bvec_iter_advance() is an overkill. Add specialised bvec_iter_advance_single() that is faster. It also handles zero-len bvecs, so can kill bvec_iter_skip_zero_bvec().
text data bss dec hex filename
before:
23977 805 0 24782 60ce lib/iov_iter.o
before, bvec_iter_advance() w/o WARN_ONCE()
22886 600 0 23486 5bbe ./lib/iov_iter.o
after:
21862 600 0 22462 57be lib/iov_iter.o

Quoted 2 lines

Reviewed-by Ming Lei <[email protected]>
Signed-off-by Pavel Begunkov <[email protected]>

Looks good,

Reviewed-by Christoph Hellwig <[email protected]>

Pavel Begunkov

author

2020-11-24 18:01 UTC #3 lore raw

PATCH 2/2 bio: optimise bvec iteration

In reply to Pavel Begunkov

__bio_for_each_bvec(), __bio_for_each_segment() and bio_copy_data_iter() fall under conditions of bvec_iter_advance_single(), which is a faster and slimmer version of bvec_iter_advance(). Add bio_advance_iter_single() and convert them.

Signed-off-by Pavel Begunkov <[email protected]>

---
 block/bio.c         |  4 ++--
 include/linux/bio.h | 17 +++++++++++++++--
 2 files changed, 17 insertions(+), 4 deletions(-)

block/bio.c +2 -2

index fa01bef35bb1..8e718920457a 100644
@@ -1212,8 +1212,8 @@ void bio_copy_data_iter(struct bio *dst, struct bvec_iter *dst_iter,
 
 		flush_dcache_page(dst_bv.bv_page);
 
-		bio_advance_iter(src, src_iter, bytes);
-		bio_advance_iter(dst, dst_iter, bytes);
+		bio_advance_iter_single(src, src_iter, bytes);
+		bio_advance_iter_single(dst, dst_iter, bytes);
 	}
 }
 EXPORT_SYMBOL(bio_copy_data_iter);

include/linux/bio.h +15 -2

index c6d765382926..d55d53c49ae4 100644
@@ -148,11 +148,24 @@ static inline void bio_advance_iter(const struct bio *bio,
 		/* TODO: It is reasonable to complete bio with error here. */
 }
 
+/* @bytes should be less or equal to bvec[i->bi_idx].bv_len */
+static inline void bio_advance_iter_single(const struct bio *bio,
+					   struct bvec_iter *iter,
+					   unsigned int bytes)
+{
+	iter->bi_sector += bytes >> 9;
+
+	if (bio_no_advance_iter(bio))
+		iter->bi_size -= bytes;
+	else
+		bvec_iter_advance_single(bio->bi_io_vec, iter, bytes);
+}
+
 #define __bio_for_each_segment(bvl, bio, iter, start)			\
 	for (iter = (start);						\
 	     (iter).bi_size &&						\
 		((bvl = bio_iter_iovec((bio), (iter))), 1);		\
-	     bio_advance_iter((bio), &(iter), (bvl).bv_len))
+	     bio_advance_iter_single((bio), &(iter), (bvl).bv_len))
 
 #define bio_for_each_segment(bvl, bio, iter)				\
 	__bio_for_each_segment(bvl, bio, iter, (bio)->bi_iter)

@@ -161,7 +174,7 @@ static inline void bio_advance_iter(const struct bio *bio,
 	for (iter = (start);						\
 	     (iter).bi_size &&						\
 		((bvl = mp_bvec_iter_bvec((bio)->bi_io_vec, (iter))), 1); \
-	     bio_advance_iter((bio), &(iter), (bvl).bv_len))
+	     bio_advance_iter_single((bio), &(iter), (bvl).bv_len))
 
 /* iterate over multi-page bvec */
 #define bio_for_each_bvec(bvl, bio, iter)			\

Signature · 1 line

2.24.0

Christoph Hellwig

2020-11-26 10:02 UTC #4 lore raw

Re: [PATCH 2/2] bio: optimise bvec iteration

Quoted 4 lines · Pavel Begunkov

__bio_for_each_bvec(), __bio_for_each_segment() and bio_copy_data_iter() fall under conditions of bvec_iter_advance_single(), which is a faster and slimmer version of bvec_iter_advance(). Add bio_advance_iter_single() and convert them.

Are you sure about bio_advance_iter()? That API looks like it might not always be limited to a single segment, and might at least need a WARN_ON_ONCE to make sure it is not abused.

Pavel Begunkov

author

2020-11-26 12:35 UTC #5 lore raw

Re: [PATCH 2/2] bio: optimise bvec iteration

Quoted 7 lines · Christoph Hellwig

Quoted 4 lines · Pavel Begunkov
__bio_for_each_bvec(), __bio_for_each_segment() and bio_copy_data_iter() fall under conditions of bvec_iter_advance_single(), which is a faster and slimmer version of bvec_iter_advance(). Add bio_advance_iter_single() and convert them.
Are you sure about bio_advance_iter()? That API looks like it might

Both those listed bio_for_each*() pass bvl.bv_len, which is truncated to current segment by bio_iter_iovec() (i.e. bvec_iter_bvec) or mp_bvec_iter_bvec().

And just to note that I didn't change bio_advance_iter() but added a new function.

There is always space for stupid mistakes, but I'm sure. What makes you to think opposite? I may have missed it.

Quoted 2 lines

not always be limited to a single segment, and might at least need a WARN_ON_ONCE to make sure it is not abused.

I thought twice about converting other places as you commented before, and it looks saner to not do that exactly for that reason. I prefer to leave *_single() versions for rare but high impact cases like for_each()s.
And as it's contained I decided to not add overhead on WARN_ONCE(), e.g. with inlining and w/o string dedup it grows .data section much.

Signature · 1 line

Pavel Begunkov

Pavel Begunkov

author

2020-12-02 13:54 UTC #6 lore raw

Re: [PATCH 2/2] bio: optimise bvec iteration

Quoted 13 lines · Pavel Begunkov

Quoted 7 lines · Christoph Hellwig
Quoted 4 lines · Pavel Begunkov
__bio_for_each_bvec(), __bio_for_each_segment() and bio_copy_data_iter() fall under conditions of bvec_iter_advance_single(), which is a faster and slimmer version of bvec_iter_advance(). Add bio_advance_iter_single() and convert them.
Are you sure about bio_advance_iter()? That API looks like it might
Both those listed bio_for_each*() pass bvl.bv_len, which is truncated to current segment by bio_iter_iovec() (i.e. bvec_iter_bvec) or mp_bvec_iter_bvec().

Quoted 5 lines

And just to note that I didn't change bio_advance_iter() but added a new function.
There is always space for stupid mistakes, but I'm sure. What makes you to think opposite? I may have missed it.

Christoph, any doubts left?

Quoted 10 lines

Quoted 2 lines
not always be limited to a single segment, and might at least need a WARN_ON_ONCE to make sure it is not abused.
I thought twice about converting other places as you commented before, and it looks saner to not do that exactly for that reason. I prefer to leave *_single() versions for rare but high impact cases like for_each()s.
And as it's contained I decided to not add overhead on WARN_ONCE(), e.g. with inlining and w/o string dedup it grows .data section much.

Signature · 1 line

Pavel Begunkov

Christoph Hellwig

Reviewed-by on v1 2/2

2020-12-02 14:57 UTC #7 lore raw

Re: [PATCH 2/2] bio: optimise bvec iteration

In reply to Pavel Begunkov

Quoted 6 lines · Pavel Begunkov

__bio_for_each_bvec(), __bio_for_each_segment() and bio_copy_data_iter() fall under conditions of bvec_iter_advance_single(), which is a faster and slimmer version of bvec_iter_advance(). Add bio_advance_iter_single() and convert them.
Signed-off-by Pavel Begunkov <[email protected]>

Looks good,

Reviewed-by Christoph Hellwig <[email protected]>

Jens Axboe

maintainer Applied

2020-12-02 16:48 UTC #8 lore raw

In reply to Pavel Begunkov

Quoted 9 lines · Pavel Begunkov

This adds simpler versions of bvec_iter_advance() and bio_advance_iter() (i.e. *_single()), that are faster but work with the restriction that @bytes shouldn't be more than available in the current bvec segment.
That covers most of bvec/bio iteration/foreach, that are massively inlined, and thus also nicely shrinks binary.
Others non core-block users might be updated on case by case basis (if applicable) after the change is merged.

Applied, thanks.

Signature · 1 line

Jens Axboe