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  1. Apr 09, 2017
  3. Apr 08, 2017
  5. Apr 07, 2017
    • NeilBrown's avatar
      block: trace completion of all bios. · fbbaf700
      NeilBrown authored 
      

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: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
      fbbaf700
    • NeilBrown's avatar
      block: simple improvements for bio->flags · dbde775c
      NeilBrown authored 
      

The comment for the 'flags' field of 'bio' mentions
"command" which is no longer stored there, and doesn't
mention the bvec pool number, which is.

BIO_RESET_BITS is set in such a way that it would need to be
updated if new bits were added, which is easy to miss.

BVEC_POOL_BITS is larger than needed.  The BVEC_POOL_IDX()
ranges from 0 to 6, so 3 bits are sufficient.

This patch make improvements in each of these areas.

Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
      dbde775c
    • Omar Sandoval's avatar
      blk-mq: remap queues when adding/removing hardware queues · ebe8bddb
      Omar Sandoval authored 
      blk_mq_update_nr_hw_queues() used to remap hardware queues, which is the
behavior that drivers expect. However, commit 4e68a011 changed
blk_mq_queue_reinit() to not remap queues for the case of CPU
hotplugging, inadvertently making blk_mq_update_nr_hw_queues() not remap
queues as well. This breaks, for example, NBD's multi-connection mode,
leaving the added hardware queues unused. Fix it by making
blk_mq_update_nr_hw_queues() explicitly remap the queues.

Fixes: 4e68a011

 ("blk-mq: don't redistribute hardware queues on a CPU hotplug event")
Reviewed-by: default avatarKeith Busch <keith.busch@intel.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarSagi Grimberg <sagi@grimberg.me>
Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
      ebe8bddb
    • Omar Sandoval's avatar
      blk-mq-sched: fix crash in switch error path · 54d5329d
      Omar Sandoval authored 
      

In elevator_switch(), if blk_mq_init_sched() fails, we attempt to fall
back to the original scheduler. However, at this point, we've already
torn down the original scheduler's tags, so this causes a crash. Doing
the fallback like the legacy elevator path is much harder for mq, so fix
it by just falling back to none, instead.

Signed-off-by: default avatarOmar Sandoval <osandov@fb.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
      54d5329d