1. 29 Nov, 2010 10 commits
  2. 28 Nov, 2010 29 commits
  3. 24 Nov, 2010 1 commit
    • Tom Herbert's avatar
      xps: Transmit Packet Steering · 1d24eb48
      Tom Herbert authored
      This patch implements transmit packet steering (XPS) for multiqueue
      devices.  XPS selects a transmit queue during packet transmission based
      on configuration.  This is done by mapping the CPU transmitting the
      packet to a queue.  This is the transmit side analogue to RPS-- where
      RPS is selecting a CPU based on receive queue, XPS selects a queue
      based on the CPU (previously there was an XPS patch from Eric
      Dumazet, but that might more appropriately be called transmit completion
      steering).
      
      Each transmit queue can be associated with a number of CPUs which will
      use the queue to send packets.  This is configured as a CPU mask on a
      per queue basis in:
      
      /sys/class/net/eth<n>/queues/tx-<n>/xps_cpus
      
      The mappings are stored per device in an inverted data structure that
      maps CPUs to queues.  In the netdevice structure this is an array of
      num_possible_cpu structures where each structure holds and array of
      queue_indexes for queues which that CPU can use.
      
      The benefits of XPS are improved locality in the per queue data
      structures.  Also, transmit completions are more likely to be done
      nearer to the sending thread, so this should promote locality back
      to the socket on free (e.g. UDP).  The benefits of XPS are dependent on
      cache hierarchy, application load, and other factors.  XPS would
      nominally be configured so that a queue would only be shared by CPUs
      which are sharing a cache, the degenerative configuration woud be that
      each CPU has it's own queue.
      
      Below are some benchmark results which show the potential benfit of
      this patch.  The netperf test has 500 instances of netperf TCP_RR test
      with 1 byte req. and resp.
      
      bnx2x on 16 core AMD
         XPS (16 queues, 1 TX queue per CPU)  1234K at 100% CPU
         No XPS (16 queues)                   996K at 100% CPU
      Signed-off-by: default avatarTom Herbert <therbert@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      1d24eb48