| Message ID | 1347322957-25260-4-git-send-email-koverstreet@google.com (mailing list archive) |
|---|---|
| State | Deferred, archived |
| Headers | show |
Hello, On Mon, Sep 10, 2012 at 05:22:14PM -0700, Kent Overstreet wrote: > static void req_bio_endio(struct request *rq, struct bio *bio, > unsigned int nbytes, int error) > { > + /* > + * XXX: bio_endio() does this. only need this because of the weird > + * flush seq thing. > + */ > if (error) > clear_bit(BIO_UPTODATE, &bio->bi_flags); > else if (!test_bit(BIO_UPTODATE, &bio->bi_flags)) > error = -EIO; Isn't this also necessary to record errors on partial completions? Other than that, I definitely like this. It would be nice to note that the custom partial bio advancing in blk_update_request() is replaced with multiple calls to req_bio_endio(). I don't think it has any meaningful performance implications. It's just nice to future readers of the commit. Also, it would be really nice if you can verify this actually works with partial blk_update_request(). sector update bug in the previous patch scares me a bit. Implementing some debug hacks in the completion path might be the easiest way to verify. A subtle bug here could be pretty painful. Thanks.
On Thu, Sep 20, 2012 at 04:20:00PM -0700, Tejun Heo wrote: > Hello, > > On Mon, Sep 10, 2012 at 05:22:14PM -0700, Kent Overstreet wrote: > > static void req_bio_endio(struct request *rq, struct bio *bio, > > unsigned int nbytes, int error) > > { > > + /* > > + * XXX: bio_endio() does this. only need this because of the weird > > + * flush seq thing. > > + */ > > if (error) > > clear_bit(BIO_UPTODATE, &bio->bi_flags); > > else if (!test_bit(BIO_UPTODATE, &bio->bi_flags)) > > error = -EIO; > > Isn't this also necessary to record errors on partial completions? Ah yeah, you're right. Meant to delete that comment anyways. > Other than that, I definitely like this. It would be nice to note > that the custom partial bio advancing in blk_update_request() is > replaced with multiple calls to req_bio_endio(). I don't think it has > any meaningful performance implications. It's just nice to future > readers of the commit. The number of calls to req_bio_endio() isn't changing... blk_update_request() called it for partial completions before. It's just where the bio itself is updated that's getting shuffled around. Or did you mean that bio_advance() is getting called on every bio instead of the custom advancing in blk_update_request() before? That is different, yeah - it's now always looping over the iovec, not just for partial completions. Yeah, I will note that in the commit message, in case Jens sees a performance regression from it :) > Also, it would be really nice if you can verify this actually works > with partial blk_update_request(). sector update bug in the previous > patch scares me a bit. Implementing some debug hacks in the > completion path might be the easiest way to verify. A subtle bug here > could be pretty painful. Any suggestions on how to trigger partial updates? -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel
Hey, On Thu, Sep 20, 2012 at 04:36:32PM -0700, Kent Overstreet wrote: > > Other than that, I definitely like this. It would be nice to note > > that the custom partial bio advancing in blk_update_request() is > > replaced with multiple calls to req_bio_endio(). I don't think it has > > any meaningful performance implications. It's just nice to future > > readers of the commit. > > The number of calls to req_bio_endio() isn't changing... > blk_update_request() called it for partial completions before. It's just > where the bio itself is updated that's getting shuffled around. > > Or did you mean that bio_advance() is getting called on every bio > instead of the custom advancing in blk_update_request() before? That is > different, yeah - it's now always looping over the iovec, not just for > partial completions. > > Yeah, I will note that in the commit message, in case Jens sees a > performance regression from it :) I don't think there's any performance implication. It's just nice to explain how the complexity went away. If for nothing else, to point out how silly the original code was. :) > > Also, it would be really nice if you can verify this actually works > > with partial blk_update_request(). sector update bug in the previous > > patch scares me a bit. Implementing some debug hacks in the > > completion path might be the easiest way to verify. A subtle bug here > > could be pretty painful. > > Any suggestions on how to trigger partial updates? ide along with many legacy drivers do it. Any SCSI driver including libata only does full completion. I don't know. Even just trying to call the function and comparing before & after with the original code would be good. I'd like to see at least some form of verification because the manifested bugs could be extremely nasty and difficult to track down. Thanks.
diff --git a/block/blk-core.c b/block/blk-core.c index 2d739ca..55c833c9 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -153,25 +153,19 @@ EXPORT_SYMBOL(blk_rq_init); static void req_bio_endio(struct request *rq, struct bio *bio, unsigned int nbytes, int error) { + /* + * XXX: bio_endio() does this. only need this because of the weird + * flush seq thing. + */ if (error) clear_bit(BIO_UPTODATE, &bio->bi_flags); else if (!test_bit(BIO_UPTODATE, &bio->bi_flags)) error = -EIO; - if (unlikely(nbytes > bio->bi_size)) { - printk(KERN_ERR "%s: want %u bytes done, %u left\n", - __func__, nbytes, bio->bi_size); - nbytes = bio->bi_size; - } - if (unlikely(rq->cmd_flags & REQ_QUIET)) set_bit(BIO_QUIET, &bio->bi_flags); - bio->bi_size -= nbytes; - bio->bi_sector += (nbytes >> 9); - - if (bio_integrity(bio)) - bio_integrity_advance(bio, nbytes); + bio_advance(bio, nbytes); /* don't actually finish bio if it's part of flush sequence */ if (bio->bi_size == 0 && !(rq->cmd_flags & REQ_FLUSH_SEQ)) @@ -2214,8 +2208,7 @@ EXPORT_SYMBOL(blk_fetch_request); **/ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes) { - int total_bytes, bio_nbytes, next_idx = 0; - struct bio *bio; + int total_bytes; if (!req->bio) return false; @@ -2259,56 +2252,21 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes) blk_account_io_completion(req, nr_bytes); - total_bytes = bio_nbytes = 0; - while ((bio = req->bio) != NULL) { - int nbytes; + total_bytes = 0; + while (req->bio) { + struct bio *bio = req->bio; + unsigned bio_bytes = min(bio->bi_size, nr_bytes); - if (nr_bytes >= bio->bi_size) { + if (bio_bytes == bio->bi_size) req->bio = bio->bi_next; - nbytes = bio->bi_size; - req_bio_endio(req, bio, nbytes, error); - next_idx = 0; - bio_nbytes = 0; - } else { - int idx = bio->bi_idx + next_idx; - - if (unlikely(idx >= bio->bi_vcnt)) { - blk_dump_rq_flags(req, "__end_that"); - printk(KERN_ERR "%s: bio idx %d >= vcnt %d\n", - __func__, idx, bio->bi_vcnt); - break; - } - - nbytes = bio_iovec_idx(bio, idx)->bv_len; - BIO_BUG_ON(nbytes > bio->bi_size); - - /* - * not a complete bvec done - */ - if (unlikely(nbytes > nr_bytes)) { - bio_nbytes += nr_bytes; - total_bytes += nr_bytes; - break; - } - /* - * advance to the next vector - */ - next_idx++; - bio_nbytes += nbytes; - } + req_bio_endio(req, bio, bio_bytes, error); - total_bytes += nbytes; - nr_bytes -= nbytes; + total_bytes += bio_bytes; + nr_bytes -= bio_bytes; - bio = req->bio; - if (bio) { - /* - * end more in this run, or just return 'not-done' - */ - if (unlikely(nr_bytes <= 0)) - break; - } + if (!nr_bytes) + break; } /* @@ -2324,16 +2282,6 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes) return false; } - /* - * if the request wasn't completed, update state - */ - if (bio_nbytes) { - req_bio_endio(req, bio, bio_nbytes, error); - bio->bi_idx += next_idx; - bio_iovec(bio)->bv_offset += nr_bytes; - bio_iovec(bio)->bv_len -= nr_bytes; - } - req->__data_len -= total_bytes; req->buffer = bio_data(req->bio);
Converts it to use bio_advance(), simplifying it quite a bit in the process. Signed-off-by: Kent Overstreet <koverstreet@google.com> CC: Jens Axboe <axboe@kernel.dk> --- block/blk-core.c | 84 +++++++++++--------------------------------------------- 1 file changed, 16 insertions(+), 68 deletions(-)