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SubjectRe: [PATCH 1/2] block: introduce BIO_IN_FLIGHT flag
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@gmail.com>
>> ---
>> 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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