1. 05 Jan, 2018 21 commits
  2. 22 Dec, 2017 1 commit
    • Jens Axboe's avatar
      blk-mq: improve heavily contended tag case · 4e5dff41
      Jens Axboe authored
      Even with a number of waitqueues, we can get into a situation where we
      are heavily contended on the waitqueue lock. I got a report on spc1
      where we're spending seconds doing this. Arguably the use case is nasty,
      I reproduce it with one device and 1000 threads banging on the device.
      But that doesn't mean we shouldn't be handling it better.
      
      What ends up happening is that a thread will fail to get a tag, add
      itself to the waitqueue, and subsequently get woken up when a tag is
      freed - only to find itself going back to sleep on the waitqueue.
      
      Instead of waking all threads, use an exclusive wait and wake up our
      sbitmap batch count instead. This seems to work well for me (massive
      improvement for this use case), and it survives basic testing. But I
      haven't fully verified it yet.
      
      An additional improvement is running the queue and checking for a new
      tag BEFORE needing to add ourselves to the waitqueue.
      Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
      4e5dff41
  3. 18 Dec, 2017 1 commit
  4. 17 Dec, 2017 17 commits