[dpdk-dev] rte_sched library performance question

[Zoltan Kiss]

On 16/02/17 20:08, Dumitrescu, Cristian wrote:
> Hi Zoltan,
>
>> -----Original Message-----
>> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Zoltan Kiss
>> Sent: Thursday, February 16, 2017 3:14 PM
>> To: dev at dpdk.org
>> Subject: [dpdk-dev] rte_sched library performance question
>>
>> Hi,
>>
>> I'm experimenting a little bit with the scheduler library, and I got some
>> performance numbers which seems to be worse than what I've expected.
>> I'm sending 64 bytes packets on a 10G interface to a separate thread, and
>> my simple test program (based on the qos_sched example) does the
>> following:
>>
>> while (1) {
>>              uint16_t ret = rte_ring_sc_dequeue_burst(it.ring,
>> (void**)flushbatch, FLUSH_SIZE);
>>              rte_mbuf** t = flushbatch;
>>
>>              if (!ret) {
>>                  /* This call is necessary to make sure the TX completed
>> mbuf's
>>                   * are returned to the pool even if there is nothing to
>>                   * transmit */
>>                  rte_eth_tx_burst(it.portid, lcore, t, 0);
>>                  continue;
>>              }
>>              rte_sched_port_enqueue(it.port, flushbatch, ret);
>>              ret = rte_sched_port_dequeue(it.port, flushbatch, FLUSH_SIZE);
> Looks to me like the scheduler dequeue burst is equal to the enqueue burst size of FLUSH_SIZE, right?
> In this case, you are always dequeueuing the exact packets that you just enqueued, and the scheduler dequeue needs to work really hard to find exactly those FLUSH_SIZE queues that each one have a single packet at this point.
>
> This is wht the enqueue burst size should be bigger than the dequeue burst size. Basically, you add some water into the reservoir up to a reasonable fill level before you start pouring it in your glass if you want to fill the glass quickly.
>
> Typical values used:
> -for vector PMD: (enqueue = 32, dequeue = 24), (32, 28), (32, 16), etc
> -for scalar PMD: (64, 48), (64, 32), ... We used (256, 248) for VPP

Thanks, it helped my case too. Btw. it would be good do link this 
document somewhere in the DPDK docs, as it contains a lot of good 
information about the scheduler:

https://networkbuilders.intel.com/docs/Network_Builders_RA_NFV_QoS_Aug2014.pdf

>
>>              while (ret) {
>>                  uint16_t n = rte_eth_tx_burst(it.portid, lcore, t, ret);
>>                  /* we cannot drop the packets, so re-send */
>>                  /* update number of packets to be sent */
>>                  ret -= n;
>>                  t = &t[n];
>>              };
>> }
>>
>> I run this on a separate thread, another one doing rx and feeding the
>> packets to the ring. When I comment out the enqueue and dequeue part in
>> the
>> code (reducing it to simple l2fwd), I can forward the entire ~14 Mpps
>> traffic, whilst with the scheduler enabled I can only reach ~5.4 Mpps at
>> best. I've tried with a single pipe or with 4k (used rand() to randomly
>> distribute between pipe, everything else (class etc) was set to 0), didn't
>> make a difference. Is this expected? I'm running this on a Xeon E5-2630 0 @
>> 2.30GHz
>>
>> I've used the following configuration:
>>
>> ; port configuration [port]
>>
>> [port]
>> frame overhead = 24
>> number of subports per port = 1
>> number of pipes per subport = 1024
>> queue sizes = 64 64 64 64
>>
>> ; Subport configuration
>>
>> [subport 0]
>> tb rate = 1250000000; Bytes per second
>> tb size = 1000000000; Bytes
>> tc 0 rate = 1250000000;     Bytes per second
>> tc 1 rate = 1250000000;     Bytes per second
>> tc 2 rate = 1250000000;     Bytes per second
>> tc 3 rate = 1250000000;     Bytes per second
>> tc period = 10;             Milliseconds
>> tc oversubscription period = 1000;     Milliseconds
>>
>> pipe 0-1024 = 0;        These pipes are configured with pipe profile 0
>>
>> ; Pipe configuration
>>
>> [pipe profile 0]
>> tb rate = 1250000000; Bytes per second
>> tb size = 1000000000; Bytes
>>
>> tc 0 rate = 1250000000; Bytes per second
>> tc 1 rate = 1250000000; Bytes per second
>> tc 2 rate = 1250000000; Bytes per second
>> tc 3 rate = 1250000000; Bytes per second
>> tc period = 10; Milliseconds
>>
>> tc 0 oversubscription weight = 1
>> tc 1 oversubscription weight = 1
>> tc 2 oversubscription weight = 1
>> tc 3 oversubscription weight = 1
>>
>> tc 0 wrr weights = 1 1 1 1
>> tc 1 wrr weights = 1 1 1 1
>> tc 2 wrr weights = 1 1 1 1
>> tc 3 wrr weights = 1 1 1 1
>>
>> Regards,
>>
>> Zoltan
> Regards,
> Cristian