Overhaul Rx path to recover from mbuf cluster allocation failure.

 o Create one more spare DMA map for Rx handler to recover from
   bus_dmamap_load_mbuf_sg(9) failure.
 o Make sure to update status bit in Rx descriptors even if we failed
   to allocate a new buffer. Previously it resulted in stuck condition
   and em_handle_rxtx task took up all available CPU cycles.
 o Don't blindly unload DMA map. Reuse loaded DMA map if received
   packet has errors. This would speed up Rx processing a bit under
   heavy load as it does not need to reload DMA map in case of error.
   (bus_dmamap_load_mbuf_sg(9) is the most expensive call in driver
    context.)
 o Update if_iqdrops counter if it can't allocate a mbuf cluster.
   With this change it's now possible to see queue dropped packets
   with netstat(1).
 o Update mbuf_cluster_failed counter if fixup code failed to
   allocate mbuf header.
 o Return ENOBUFS instead of ENOMEM in case of Rx fixup failure.
 o Make adapter->lmp NULL in case of Rx fixup failure. Strictly
   specking it's not necessary for correct operation but it makes
   the intention clear.
 o Remove now unused dropped_pkts member in softc.

With these changes em(4) should survive mbuf cluster allocation
failure on Rx path.

Reviewed by:	pdeuskar, glebius (with improvements)

0 files changed, 0 insertions, 0 deletions