1. 24 1月, 2013 1 次提交
    • B
      net: cdc_mbim: send ZLP only for the specific buggy device · 844e88f0
      Bjørn Mork 提交于
      Reverting 328d7b8a and instead adding an exception for the
      Sierra Wireless MC7710.
      
      commit 328d7b8a (net: cdc_mbim: send ZLP after max sized NTBs)
      added a workaround for an issue observed on one specific device.
      Concerns were raised that this workaround adds a performance
      penalty to all devices based on questionable, if not buggy,
      behaviour of a single device:
      
       "If you add ZLP for NTBs of dwNtbOutMaxSize, you are heavily affecting CPU
        load, increasing interrupt load by factor of 2 in high load traffic
        scenario and possibly decreasing throughput for all other devices
        which behaves correctly."
      
       "The idea of NCM was to avoid extra ZLPs. If your transfer is exactly
        dwNtbOutMaxSize, it's known, you can submit such request on the receiver
        side and you do not need any EOT indicatation, so the frametime can be
        used for useful data."
      
      Adding a device specific exception to prevent the workaround from
      affecting well behaved devices.
      
      The assumption here is that needing a ZLP is truly an *exception*.
      We do not yet have enough data to verify this.  The generic
      workaround in commit 328d7b8a should be considered acceptable despite
      the performance penalty if the exception list becomes a maintainance
      hassle.
      
      Cc: Alexey ORISHKO <alexey.orishko@stericsson.com>
      Cc: Yauheni Kaliuta <y.kaliuta@gmail.com>
      Signed-off-by: NBjørn Mork <bjorn@mork.no>
      Signed-off-by: NDavid S. Miller <davem@davemloft.net>
      844e88f0
  2. 23 1月, 2013 4 次提交
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