Re: NIC Stops Transmitting

[Scott Talbert <swt-HdGmbYkwPlSsTnJN9+BGXg@public.gmane.org>]

On Fri, 26 Jul 2013, Stephen Hemminger wrote:

>> I'm writing an application using DPDK that transmits a large number of
>> packets (it doesn't receive any).  When I transmit at 2 Gb/sec, everything
>> will run fine for several seconds (receiver is receiving at correct rate),
>> but then the NIC appears to get 'stuck' and doesn't transmit any more
>> packets.  In this state, rte_eth_tx_burst() is returning zero (suggesting
>> that there are no available transmit descriptors), but even if I sleep()
>> for a second and try again, rte_eth_tx_burst() still returns 0.  It almost
>> appears as if a packet gets stuck in the transmit ring and keeps
>> everything from flowing.  I'm using an Intel 82599EB NIC.
>>
> Make sure there is enough memory for mbufs.
> Also what is your ring size and transmit free threshold?
> It is easy to instrument the driver to see where it is saying "no space left"
> Also be careful with threshold values, many values of pthresh/hthresh/wthresh
> don't work. I would check the Intel reference manual for your hardware.

Thanks for the tips.  I don't think I'm running out of mbufs, but I'll 
check that again.  I am using these values from one of the examples - 
which claim to be correct for the 82599EB.

/*
  * These default values are optimized for use with the Intel(R) 82599 10 
GbE
  * Controller and the DPDK ixgbe PMD. Consider using other values for 
other
  * network controllers and/or network drivers.
  */
#define TX_PTHRESH 36 /**< Default values of TX prefetch threshold reg. */
#define TX_HTHRESH 0  /**< Default values of TX host threshold reg. */
#define TX_WTHRESH 0  /**< Default values of TX write-back threshold reg. 
*/

static const struct rte_eth_txconf tx_conf = {
     .tx_thresh = {
         .pthresh = TX_PTHRESH,
         .hthresh = TX_HTHRESH,
         .wthresh = TX_WTHRESH,
     },
     .tx_free_thresh = 0, /* Use PMD default values */
     .tx_rs_thresh = 0, /* Use PMD default values */
};

/*
  * Configurable number of RX/TX ring descriptors
  */
#define RTE_TEST_TX_DESC_DEFAULT 512
static uint16_t nb_txd = RTE_TEST_TX_DESC_DEFAULT;