| Message ID | 20240826173820.1690925-5-hch@lst.de (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [1/4] block: rework bio splitting | expand |
On 8/27/24 02:37, Christoph Hellwig wrote: > bio_split_rw is designed to split read and write bios with a payload. > Currently it is called by __bio_split_to_limits for all operations not > explicitly list, which works because bio_may_need_split explicitly checks > for bi_vcnt == 1 and thus skips the bypass if there is no payload and > bio_for_each_bvec loop will never execute it's body if bi_size is 0. > > But all this is hard to understand, fragile and wasted pointless cycles. > Switch __bio_split_to_limits to only call bio_split_rw for READ and > WRITE command and don't attempt any kind split for operation that do not > require splitting. > > Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
diff --git a/block/blk.h b/block/blk.h index 61c2afa67daabb..32f4e9f630a3ac 100644 --- a/block/blk.h +++ b/block/blk.h @@ -372,7 +372,8 @@ static inline struct bio *__bio_split_to_limits(struct bio *bio, const struct queue_limits *lim, unsigned int *nr_segs) { switch (bio_op(bio)) { - default: + case REQ_OP_READ: + case REQ_OP_WRITE: if (bio_may_need_split(bio, lim)) return bio_split_rw(bio, lim, nr_segs); *nr_segs = 1; @@ -384,6 +385,10 @@ static inline struct bio *__bio_split_to_limits(struct bio *bio, return bio_split_discard(bio, lim, nr_segs); case REQ_OP_WRITE_ZEROES: return bio_split_write_zeroes(bio, lim, nr_segs); + default: + /* other operations can't be split */ + *nr_segs = 0; + return bio; } }
bio_split_rw is designed to split read and write bios with a payload. Currently it is called by __bio_split_to_limits for all operations not explicitly list, which works because bio_may_need_split explicitly checks for bi_vcnt == 1 and thus skips the bypass if there is no payload and bio_for_each_bvec loop will never execute it's body if bi_size is 0. But all this is hard to understand, fragile and wasted pointless cycles. Switch __bio_split_to_limits to only call bio_split_rw for READ and WRITE command and don't attempt any kind split for operation that do not require splitting. Signed-off-by: Christoph Hellwig <hch@lst.de> --- block/blk.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)