svn commit: r273112 - head/sys/dev/ixgbe

[Ryan Stone]

On Thu, Nov 6, 2014 at 12:21 PM, Adrian Chadd <adrian at freebsd.org> wrote:
> Hm, are there any other hardware counters that we can use to see what
> was dropped?

On the 82599 and later you need to configure the RQSMR register to map
queue pools to indices and then the QPRDC[i] register will contain the
number of drops.

Note that the 82598 doesn't support the DROPEN bit in the SRRCTL
register.  There is a separate DROPEN register on the 82598, but I
have the following worrisome comment in my version of ixgbe:

    if (hw->mac.type == ixgbe_mac_82598EB) {
        /*
         * The DROPEN register is intended to allow us to immediately
         * drop packets that cannot be DMA'ed to memory right away to
         * avoid head-of-line blocking.  However we have observed that
         * enabling this functionality can lead to situations where a
         * queue will drop every packet destined for it silently, so
         * we instead accept the HOL blocking and disable the immediate
         * dropping
         */
        IXGBE_WRITE_REG(&adapter->hw, IXGBE_DROPEN, 0);