---
- branch: MAIN
  date: Fri Jun 28 15:08:47 UTC 2019
  files:
  - new: '1.44'
    old: '1.43'
    path: src/sys/dev/ic/nvme.c
    pathrev: src/sys/dev/ic/nvme.c@1.44
    type: modified
  - new: '1.20'
    old: '1.19'
    path: src/sys/dev/ic/nvmevar.h
    pathrev: src/sys/dev/ic/nvmevar.h@1.20
    type: modified
  id: 20190628T150847Z.982dec82ebd0579dbc8cca87e37a4bb37593a0e0
  log: "Fix a performance issue where one busy queue can starve all other queues.\n\nIn
    normal operations with multiple queues, the nvme driver will attempt\nto schedule
    I/O requests on the submitting CPU. This breaks down when any\none of the queues
    becomes full; the driver returns EAGAIN to the disk\nlayer, which causes the disk
    layer to stop submitting more requests until\nthe blocked request is consumed.
    When space becomes available in the full\nqueue, it pulls the next buffer from
    the bufq and fills the queue again,\nuntil finally hitting EAGAIN and preventing
    other queues from processing\nrequests.\n\nTwo changes here to fix the problem:\n\n
    - When processing requests from the bufq, attempt to assign them to the\n   queue
    associated with the CPU that originated the request.\n - If that queue is busy,
    try to find another queue with available space\n   before returning EAGAIN. This
    way, only when all queues are full will\n   the disk layer stop submitting more
    requests.\n\nNow for some real numbers. On a Rockchip RK3399 board (6 CPUs), with
    6\nconcurrent readers:\n\nOld code:\n\t4294967296 bytes transferred in 52.420
    secs (81933752 bytes/sec)\n\t4294967296 bytes transferred in 53.969 secs (79582117
    bytes/sec)\n\t4294967296 bytes transferred in 55.391 secs (77539082 bytes/sec)\n\t4294967296
    bytes transferred in 55.649 secs (77179595 bytes/sec)\n\t4294967296 bytes transferred
    in 56.102 secs (76556402 bytes/sec)\n\t4294967296 bytes transferred in 72.901
    secs (58915066 bytes/sec)\n\nNew code:\n\t4294967296 bytes transferred in 37.171
    secs (115546186 bytes/sec)\n\t4294967296 bytes transferred in 37.611 secs (114194445
    bytes/sec)\n\t4294967296 bytes transferred in 37.655 secs (114061009 bytes/sec)\n\t4294967296
    bytes transferred in 38.247 secs (112295534 bytes/sec)\n\t4294967296 bytes transferred
    in 38.496 secs (111569183 bytes/sec)\n\t4294967296 bytes transferred in 38.595
    secs (111282997 bytes/sec)\n"
  module: src
  subject: 'CVS commit: src/sys/dev/ic'
  unixtime: '1561734527'
  user: jmcneill