"TX WTHRESH must be set to 0 if tx_rs_thresh is greater than 1"

[Matthew Hall <mhall-Hv3ogNYU3JfZZajBQzqCxQ@public.gmane.org>]

Hello,

I'm just trying to understand what you're supposed to do about this error to 
get the optiomal configuration / performance. The error message and comments 
seem like they're designed for Intel ethernet driver hackers not security 
hackers like myself! ;-)

Note: I'm trying out the Intel 82545EM in VirtualBox because the virtio-net 
approach didn't work, for reasons I enumerated in some previous mails.

    /*
     * If rs_bit_thresh is greater than 1, then TX WTHRESH should be
     * set to 0. If WTHRESH is greater than zero, the RS bit is ignored
     * by the NIC and all descriptors are written back after the NIC
     * accumulates WTHRESH descriptors.
     */
    if (tx_conf->tx_thresh.wthresh != 0 && tx_rs_thresh != 1) {
        RTE_LOG(ERR, PMD, "TX WTHRESH must be set to 0 if "
            "tx_rs_thresh is greater than 1. (tx_rs_thresh=%u "
            "port=%d queue=%d)\n", (unsigned int)tx_rs_thresh,
                (int)dev->data->port_id, (int)queue_idx);
        return -(EINVAL);
    }

Thanks,
Matthew.