Re: [RFC] l2fwd: trying to expose eth_igb_xmit_pkts unusual behavior

[ciprian.barbu <ciprian.barbu@enea.com>]

ping

On 24.07.2015 15:59, Zoltan Kiss wrote:
> Hi,
>
> On 24/07/15 11:13, Ciprian Barbu wrote:
>> From: Ciprian Barbu <ciprian.barbu@enea.com>
>>
>> This tries to show an approximate behavior described in an earlier
>> discussion
>> called "can eth_igb_xmit_pkts called with len 0 affect transmission?"
>>
>> I'm using Intel i350 dual port 1Gb card and I've tweaked the pool size
>> to the
>> minimum possible. But unmodified l2fwd still worked withouth a sweat.
>> After
>> applying this patch transmission stopped after maybe 30 seconds.
>> Lowering the
>> 'magic' number causes l2fwd to stop sending packets even earlier.
>> Using gdb I could see eth_igb_xmit_pkts always returning because nb_tx
>> was 0
>> and E1000_TXD_STAT_DD was not set (approx igb_rxtx.c : 476)
>
> I think the proper solution for this will be to introduce an explicit
> API which makes it possible for the application to call the actual PMD's
> callback function, which flushes out the completed buffers from the TX
> ring, if possible. Then in case of igb it could be a noop. See the
> discussion in this thread:

What I' trying to show here is an unexpected behavior in the tx routine 
of the igb pmd. The documentation doesn't mention that making this call 
with 0 nb_pkt can cause undefined behavior. It would be nice if someone 
could take a look at this.

>
> http://dpdk.org/ml/archives/dev/2015-June/018487.html
>
> I'll plan to propose such API, but it won't be in the very near future,
> as 2.1 will come out soon and no new features accepted at the moment.
> For the short term we can introduce a check in ODP-DPDK, which avoids
> this rte_eth_tx_burst(..., 0) call if the PMD is igb. How about that?
>
>
>>
>> Signed-off-by: Ciprian Barbu <ciprian.barbu@enea.com>
>> ---
>>   examples/l2fwd/main.c | 13 +++++++++++--
>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/examples/l2fwd/main.c b/examples/l2fwd/main.c
>> index 17621ee..623b836 100644
>> --- a/examples/l2fwd/main.c
>> +++ b/examples/l2fwd/main.c
>> @@ -72,7 +72,7 @@
>>   #define RTE_LOGTYPE_L2FWD RTE_LOGTYPE_USER1
>>
>>   #define MBUF_SIZE (2048 + sizeof(struct rte_mbuf) +
>> RTE_PKTMBUF_HEADROOM)
>> -#define NB_MBUF   8192
>> +#define NB_MBUF   1024
>>
>>   #define MAX_PKT_BURST 32
>>   #define BURST_TX_DRAIN_US 100 /* TX drain every ~100us */
>> @@ -260,7 +260,7 @@ l2fwd_main_loop(void)
>>       struct rte_mbuf *m;
>>       unsigned lcore_id;
>>       uint64_t prev_tsc, diff_tsc, cur_tsc, timer_tsc;
>> -    unsigned i, j, portid, nb_rx;
>> +    unsigned i, j, portid, nb_rx, magic = 0;
>>       struct lcore_queue_conf *qconf;
>>       const uint64_t drain_tsc = (rte_get_tsc_hz() + US_PER_S - 1) /
>> US_PER_S * BURST_TX_DRAIN_US;
>>
>> @@ -285,6 +285,15 @@ l2fwd_main_loop(void)
>>       }
>>
>>       while (1) {
>> +        if (++magic == 50000) {
>> +            magic = 0;
>> +            l2fwd_send_burst(&lcore_queue_conf[lcore_id],
>> +                     0,
>> +                     (uint8_t) 0);
>> +            l2fwd_send_burst(&lcore_queue_conf[lcore_id],
>> +                     0,
>> +                     (uint8_t) 1);
>> +        }
>>
>>           cur_tsc = rte_rdtsc();
>>
>>