[dpdk-dev] [RFC] l2fwd: trying to expose eth_igb_xmit_pkts unusual behavior
ciprian.barbu
ciprian.barbu at enea.com
Mon Aug 3 11:32:35 CEST 2015
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 at 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 at 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();
>>
>>
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