Re: [PATCH 1/2] block: introduce BIO_IN_FLIGHT flag

[Namhyung Kim]

2012-01-09 10:56 AM, Tejun Heo wrote:
> On Tue, Dec 27, 2011 at 11:28:32PM +0900, Namhyung Kim wrote:
> > BIO_IN_FLIGHT flag is used for tracing block I/O completion.
> > This patch fixes tracing bio-based devices - except DM which
> > inserts completion tracepoint explicitly - that could not be
> > traced such event using blktrace.
> >
> > It won't affect tracing normal (request-based) disk devices
> > and nested bio handling paths.
> >
> > Signed-off-by: Namhyung Kim<namhyung@xxxxxxxxx>
> > ---
> >   block/blk-core.c          |    5 +++++
> >   fs/bio.c                  |    7 +++++++
> >   include/linux/blk_types.h |    1 +
> >   3 files changed, 13 insertions(+), 0 deletions(-)
> >
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index 1b4fd93af2c0..f61310323954 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -165,6 +165,9 @@ static void req_bio_endio(struct request *rq, struct bio *bio,
> >   	if (unlikely(rq->cmd_flags&  REQ_QUIET))
> >   		set_bit(BIO_QUIET,&bio->bi_flags);
> >
> > +	/* completion event was already reported in blk_update_request */
> > +	clear_bit(BIO_IN_FLIGHT,&bio->bi_flags);
> > +
> >   	bio->bi_size -= nbytes;
> >   	bio->bi_sector += (nbytes>>  9);
> >
> > @@ -1662,6 +1665,8 @@ void generic_make_request(struct bio *bio)
> p>   	do {
> >   		struct request_queue *q = bdev_get_queue(bio->bi_bdev);
> >
> > +		set_bit(BIO_IN_FLIGHT,&bio->bi_flags);
> > +
> >   		q->make_request_fn(q, bio);
> >
> >   		bio = bio_list_pop(current->bio_list);
> > diff --git a/fs/bio.c b/fs/bio.c
> > index b1fe82cf88cf..10fb7a1d74ba 100644
> > --- a/fs/bio.c
> > +++ b/fs/bio.c
> > @@ -1447,6 +1447,13 @@ void bio_endio(struct bio *bio, int error)
> >   	else if (!test_bit(BIO_UPTODATE,&bio->bi_flags))
> >   		error = -EIO;
> >
> > +	if (test_bit(BIO_IN_FLIGHT,&bio->bi_flags)) {
> > +		struct request_queue *q = bdev_get_queue(bio->bi_bdev);
> > +
> > +		trace_block_bio_complete(q, bio, error);
> > +		clear_bit(BIO_IN_FLIGHT,&bio->bi_flags);
> > +	}
>
> This really should be filtered from the consumer side.  Not on TP
> itself.  Doing it like this makes the TP useless for other consumers
> and adds unnecessary flag and operations on it even when the TP is not
> in use.  Why not just trigger the TP on boi_endio() and let blktrace
> probe filter out bounced or cloned completions?

I understand your concerns. However, the blktrace cannot get 
bio->bi_flags info in its current form AFAIK. Doing it will require 
extending struct blk_io_trace and it'll cause a compatibility issue,
I guess.

Anyway I think the needs of tracing bio based drivers are growing so 
it'd be great the blktrace supports it as well. Also as we've run out of 
act_mask bits, it might be needed a room for extending.

But before proceeding, I'd like to listen comments/advices from people. 
Jens?

Thanks,
Namhyung Kim
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