On Thu, Sep 20, 2012 at 04:41:33PM -0700, Tejun Heo wrote:
Hey,
On Thu, Sep 20, 2012 at 04:36:32PM -0700, Kent Overstreet wrote:
quoted
quoted
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. :)
New patch below - that commit message have what you're after?
quoted
quoted
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.
Multiple partial completions should have the same semantics as a single
full completion, so maybe I'll try rigging up some test code that wraps
blk_update_request(), turning full completions into partial completions,
and verifies stuff...
commit fef0ddc82214f87de71ec6fb051eb28a6de0be74
Author: Kent Overstreet [off-list ref]
Date: Thu Sep 20 16:38:30 2012 -0700
block: Refactor blk_update_request()
Converts it to use bio_advance(), simplifying it quite a bit in the
process.
Note that req_bio_endio() now always calls bio_advance() - which means
it always loops over the biovec, not just on partial completions. Don't
expect it to affect performance, but worth noting.
Signed-off-by: Kent Overstreet [off-list ref]
CC: Jens Axboe [off-list ref]
diff --git a/block/blk-core.c b/block/blk-core.c
index 2d739ca..9f8cb16 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -158,20 +158,10 @@ static void req_bio_endio(struct request *rq, struct bio *bio,
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 +2204,7 @@ 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 +2248,21 @@ 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 +2278,6 @@ 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);