• Jan Kara's avatar
    blktrace: Provide event for request merging · f3bdc62f
    Jan Kara authored
    Currently blk-mq does not report any event when two requests get merged
    in the elevator. This then results in difficult to understand sequence
    of events like:
    
    ...
      8,0   34     1579     0.608765271  2718  I  WS 215023504 + 40 [dbench]
      8,0   34     1584     0.609184613  2719  A  WS 215023544 + 56 <- (8,4) 2160568
      8,0   34     1585     0.609184850  2719  Q  WS 215023544 + 56 [dbench]
      8,0   34     1586     0.609188524  2719  G  WS 215023544 + 56 [dbench]
      8,0    3      602     0.609684162   773  D  WS 215023504 + 96 [kworker/3:1H]
      8,0   34     1591     0.609843593     0  C  WS 215023504 + 96 [0]
    
    and you can only guess (after quite some headscratching since the above
    excerpt is intermixed with a lot of other IO) that request 215023544+56
    got merged to request 215023504+40. Provide proper event for request
    merging like we used to do in the legacy block layer.
    Signed-off-by: default avatarJan Kara <jack@suse.cz>
    Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
    f3bdc62f
block.h 17.5 KB