lkml.org 
[lkml]   [2017]   [Mar]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v3] block: trace completion of all bios.
    On Fri, Mar 24, 2017 at 8:07 AM, NeilBrown <neilb@suse.com> wrote:
    >
    > Currently only dm and md/raid5 bios trigger
    > trace_block_bio_complete(). Now that we have bio_chain() and
    > bio_inc_remaining(), it is not possible, in general, for a driver to
    > know when the bio is really complete. Only bio_endio() knows that.
    >
    > So move the trace_block_bio_complete() call to bio_endio().
    >
    > Now trace_block_bio_complete() pairs with trace_block_bio_queue().
    > Any bio for which a 'queue' event is traced, will subsequently
    > generate a 'complete' event.
    >
    > There are a few cases where completion tracing is not wanted.
    > 1/ If blk_update_request() has already generated a completion
    > trace event at the 'request' level, there is no point generating
    > one at the bio level too. In this case the bi_sector and bi_size
    > will have changed, so the bio level event would be wrong
    >
    > 2/ If the bio hasn't actually been queued yet, but is being aborted
    > early, then a trace event could be confusing. Some filesystems
    > call bio_endio() but do not want tracing.
    >
    > 3/ The bio_integrity code interposes itself by replacing bi_end_io,
    > then restoring it and calling bio_endio() again. This would produce
    > two identical trace events if left like that.
    >
    > To handle these, we introduce a flag BIO_TRACE_COMPLETION and only
    > produce the trace event when this is set.
    > We address point 1 above by clearing the flag in blk_update_request().
    > We address point 2 above by only setting the flag when
    > generic_make_request() is called.
    > We address point 3 above by clearing the flag after generating a
    > completion event.
    >
    > When bio_split() is used on a bio, particularly in blk_queue_split(),
    > there is an extra complication. A new bio is split off the front, and
    > may be handle directly without going through generic_make_request().
    > The old bio, which has been advanced, is passed to
    > generic_make_request(), so it will trigger a trace event a second
    > time.
    > Probably the best result when a split happens is to see a single
    > 'queue' event for the whole bio, then multiple 'complete' events - one
    > for each component. To achieve this was can:
    > - copy the BIO_TRACE_COMPLETION flag to the new bio in bio_split()
    > - avoid generating a 'queue' event if BIO_TRACE_COMPLETION is already set.
    > This way, the split-off bio won't create a queue event, the original
    > won't either even if it re-submitted to generic_make_request(),
    > but both will produce completion events, each for their own range.
    >
    > So if generic_make_request() is called (which generates a QUEUED
    > event), then bi_endio() will create a single COMPLETE event for each
    > range that the bio is split into, unless the driver has explicitly
    > requested it not to.
    >
    > Signed-off-by: NeilBrown <neilb@suse.com>
    > ---
    > block/bio.c | 13 +++++++++++++
    > block/blk-core.c | 10 +++++++++-
    > drivers/md/dm.c | 1 -
    > drivers/md/raid5.c | 8 --------
    > include/linux/blk_types.h | 4 +++-
    > 5 files changed, 25 insertions(+), 11 deletions(-)
    >
    > diff --git a/block/bio.c b/block/bio.c
    > index 5eec5e08417f..c1272986133e 100644
    > --- a/block/bio.c
    > +++ b/block/bio.c
    > @@ -1818,6 +1818,11 @@ static inline bool bio_remaining_done(struct bio *bio)
    > * bio_endio() will end I/O on the whole bio. bio_endio() is the preferred
    > * way to end I/O on a bio. No one should call bi_end_io() directly on a
    > * bio unless they own it and thus know that it has an end_io function.
    > + *
    > + * bio_endio() can be called several times on a bio that has been chained
    > + * using bio_chain(). The ->bi_end_io() function will only be call the
    > + * last time. At this point the BLK_TA_COMPLETE tracing event will be
    > + * generated if BIO_TRACE_COMPLETION is set.
    > **/
    > void bio_endio(struct bio *bio)
    > {
    > @@ -1838,6 +1843,11 @@ void bio_endio(struct bio *bio)
    > goto again;
    > }
    >
    > + if (bio->bi_bdev && bio_flagged(bio, BIO_TRACE_COMPLETION)) {
    > + trace_block_bio_complete(bdev_get_queue(bio->bi_bdev),
    > + bio, bio->bi_error);
    > + bio_clear_flag(bio, BIO_TRACE_COMPLETION);
    > + }
    > if (bio->bi_end_io)
    > bio->bi_end_io(bio);
    > }
    > @@ -1876,6 +1886,9 @@ struct bio *bio_split(struct bio *bio, int sectors,
    >
    > bio_advance(bio, split->bi_iter.bi_size);
    >
    > + if (bio_flagged(bio, BIO_TRACE_COMPLETION))
    > + bio_set_flag(bio, BIO_TRACE_COMPLETION);
    > +
    > return split;
    > }
    > EXPORT_SYMBOL(bio_split);
    > diff --git a/block/blk-core.c b/block/blk-core.c
    > index 0eeb99ef654f..b34b5b1b1bbf 100644
    > --- a/block/blk-core.c
    > +++ b/block/blk-core.c
    > @@ -1936,7 +1936,13 @@ generic_make_request_checks(struct bio *bio)
    > if (!blkcg_bio_issue_check(q, bio))
    > return false;
    >
    > - trace_block_bio_queue(q, bio);
    > + if (!bio_flagged(bio, BIO_TRACE_COMPLETION)) {
    > + trace_block_bio_queue(q, bio);
    > + /* Now that enqueuing has been traced, we need to trace
    > + * completion as well.
    > + */
    > + bio_set_flag(bio, BIO_TRACE_COMPLETION);
    > + }
    > return true;
    >
    > not_supported:
    > @@ -2595,6 +2601,8 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
    > if (bio_bytes == bio->bi_iter.bi_size)
    > req->bio = bio->bi_next;
    >
    > + /* Completion has already been traced */
    > + bio_clear_flag(bio, BIO_TRACE_COMPLETION);
    > req_bio_endio(req, bio, bio_bytes, error);
    >
    > total_bytes += bio_bytes;
    > diff --git a/drivers/md/dm.c b/drivers/md/dm.c
    > index f4ffd1eb8f44..f5f09ace690a 100644
    > --- a/drivers/md/dm.c
    > +++ b/drivers/md/dm.c
    > @@ -810,7 +810,6 @@ static void dec_pending(struct dm_io *io, int error)
    > queue_io(md, bio);
    > } else {
    > /* done with normal IO or empty flush */
    > - trace_block_bio_complete(md->queue, bio, io_error);
    > bio->bi_error = io_error;
    > bio_endio(bio);
    > }
    > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
    > index 9a3b7da34137..f684cb566721 100644
    > --- a/drivers/md/raid5.c
    > +++ b/drivers/md/raid5.c
    > @@ -5141,8 +5141,6 @@ static void raid5_align_endio(struct bio *bi)
    > rdev_dec_pending(rdev, conf->mddev);
    >
    > if (!error) {
    > - trace_block_bio_complete(bdev_get_queue(raid_bi->bi_bdev),
    > - raid_bi, 0);
    > bio_endio(raid_bi);
    > if (atomic_dec_and_test(&conf->active_aligned_reads))
    > wake_up(&conf->wait_for_quiescent);
    > @@ -5727,10 +5725,6 @@ static void raid5_make_request(struct mddev *mddev, struct bio * bi)
    > md_write_end(mddev);
    > remaining = raid5_dec_bi_active_stripes(bi);
    > if (remaining == 0) {
    > -
    > -
    > - trace_block_bio_complete(bdev_get_queue(bi->bi_bdev),
    > - bi, 0);
    > bio_endio(bi);
    > }
    > }
    > @@ -6138,8 +6132,6 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
    > }
    > remaining = raid5_dec_bi_active_stripes(raid_bio);
    > if (remaining == 0) {
    > - trace_block_bio_complete(bdev_get_queue(raid_bio->bi_bdev),
    > - raid_bio, 0);
    > bio_endio(raid_bio);
    > }
    > if (atomic_dec_and_test(&conf->active_aligned_reads))
    > diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
    > index d703acb55d0f..db7a57ee0e58 100644
    > --- a/include/linux/blk_types.h
    > +++ b/include/linux/blk_types.h
    > @@ -29,7 +29,7 @@ struct bio {
    > * top bits REQ_OP. Use
    > * accessors.
    > */
    > - unsigned short bi_flags; /* status, command, etc */
    > + unsigned short bi_flags; /* status, etc */
    > unsigned short bi_ioprio;
    >
    > struct bvec_iter bi_iter;
    > @@ -102,6 +102,8 @@ struct bio {
    > #define BIO_REFFED 8 /* bio has elevated ->bi_cnt */
    > #define BIO_THROTTLED 9 /* This bio has already been subjected to
    > * throttling rules. Don't do it again. */
    > +#define BIO_TRACE_COMPLETION 10 /* bio_endio() should trace the final completion
    > + * of this bio. */

    This may not be a good idea, since the flag space is quite small(12).

    Thanks,
    Ming

    \
     
     \ /
      Last update: 2017-03-24 07:48    [W:2.497 / U:0.456 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site