From fbbaf700e7b163a0f1704b2d542ee28be11fce21 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Fri, 7 Apr 2017 09:40:52 -0600 Subject: block: trace completion of all bios. 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 Signed-off-by: Jens Axboe --- block/bio.c | 14 ++++++++++++++ block/blk-core.c | 10 +++++++++- 2 files changed, 23 insertions(+), 1 deletion(-) (limited to 'block') diff --git a/block/bio.c b/block/bio.c index f1857c0f0826..f4d207180266 100644 --- a/block/bio.c +++ b/block/bio.c @@ -1826,6 +1826,11 @@ 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 called 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) { @@ -1846,6 +1851,12 @@ again: 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); + } + blk_throtl_bio_endio(bio); if (bio->bi_end_io) bio->bi_end_io(bio); @@ -1885,6 +1896,9 @@ 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 316a5399fb15..8654aa0cef6d 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -1957,7 +1957,13 @@ 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: @@ -2622,6 +2628,8 @@ 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; -- cgit v1.2.3