Re: rte_sched library performance question

On 16/02/17 20:08, Dumitrescu, Cristian wrote:

Hi Zoltan,

quoted

-----Original Message-----
From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Zoltan Kiss
Sent: Thursday, February 16, 2017 3:14 PM
To: dev@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

quoted

             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