[dpdk-dev] [External] Re: [PATCH v2] app/testpmd: flowgen support ip and udp fields

[Ferruh Yigit]

On 8/11/2021 3:48 AM, 王志宏 wrote:
> On Tue, Aug 10, 2021 at 5:12 PM Ferruh Yigit <ferruh.yigit at intel.com> wrote:
>>
>> On 8/10/2021 8:57 AM, 王志宏 wrote:
>>> Thanks for the review Ferruh :)
>>>
>>> On Mon, Aug 9, 2021 at 11:18 PM Ferruh Yigit <ferruh.yigit at intel.com> wrote:
>>>>
>>>> On 8/9/2021 7:52 AM, Zhihong Wang wrote:
>>>>> This patch aims to:
>>>>>  1. Add flexibility by supporting IP & UDP src/dst fields
>>>>
>>>> What is the reason/"use case" of this flexibility?
>>>
>>> The purpose is to emulate pkt generator behaviors.
>>>
>>
>> 'flowgen' forwarding is already to emulate pkt generator, but it was only
>> changing destination IP.
>>
>> What additional benefit does changing udp ports of the packets brings? What is
>> your usecase for this change?
> 
> Pkt generators like pktgen/trex/ixia/spirent can change various fields
> including ip/udp src/dst.
> 

But testpmd is not packet generator, it has very simple 'flowgen' forwarding
engine, I would like to understand motivation to make it more complex.

> Keeping the cfg_n_* while setting cfg_n_ip_dst = 1024 and others = 1
> makes the default behavior exactly unchanged. Do you think it makes
> sense?
> 
>>
>>>>
>>>>>  2. Improve multi-core performance by using per-core vars>
>>>>
>>>> On multi core this also has syncronization problem, OK to make it per-core. Do
>>>> you have any observed performance difference, if so how much is it?
>>>
>>> Huge difference, one example: 8 core flowgen -> rxonly results: 43
>>> Mpps (per-core) vs. 9.3 Mpps (shared), of course the numbers "varies
>>> depending on system configuration".
>>>
>>
>> Thanks for clarification.
>>
>>>>
>>>> And can you please separate this to its own patch? This can be before ip/udp update.
>>>
>>> Will do.
>>>
>>>>
>>>>> v2: fix assigning ip header cksum
>>>>>
>>>>
>>>> +1 to update, can you please make it as seperate patch?
>>>
>>> Sure.
>>>
>>>>
>>>> So overall this can be a patchset with 4 patches:
>>>> 1- Fix retry logic (nb_rx -> nb_pkt)
>>>> 2- Use 'rte_ipv4_cksum()' API (instead of static 'ip_sum()')
>>>> 3- User per-core varible (for 'next_flow')
>>>> 4- Support ip/udp src/dst variaty of packets
>>>>
>>>
>>> Great summary. Thanks a lot.
>>>
>>>>> Signed-off-by: Zhihong Wang <wangzhihong.wzh at bytedance.com>
>>>>> ---
>>>>>  app/test-pmd/flowgen.c | 137 +++++++++++++++++++++++++++++++------------------
>>>>>  1 file changed, 86 insertions(+), 51 deletions(-)
>>>>>
>>>>
>>>> <...>
>>>>
>>>>> @@ -185,30 +193,57 @@ pkt_burst_flow_gen(struct fwd_stream *fs)
>>>>>               }
>>>>>               pkts_burst[nb_pkt] = pkt;
>>>>>
>>>>> -             next_flow = (next_flow + 1) % cfg_n_flows;
>>>>> +             if (++next_udp_dst < cfg_n_udp_dst)
>>>>> +                     continue;
>>>>> +             next_udp_dst = 0;
>>>>> +             if (++next_udp_src < cfg_n_udp_src)
>>>>> +                     continue;
>>>>> +             next_udp_src = 0;
>>>>> +             if (++next_ip_dst < cfg_n_ip_dst)
>>>>> +                     continue;
>>>>> +             next_ip_dst = 0;
>>>>> +             if (++next_ip_src < cfg_n_ip_src)
>>>>> +                     continue;
>>>>> +             next_ip_src = 0;
>>>>
>>>> What is the logic here, can you please clarifiy the packet generation logic both
>>>> in a comment here and in the commit log?
>>>
>>> It's round-robin field by field. Will add the comments.
>>>
>>
>> Thanks. If the receiving end is doing RSS based on IP address, dst address will
>> change in every 100 packets and src will change in every 10000 packets. This is
>> a slight behavior change.
>>
>> When it was only dst ip, it was simple to just increment it, not sure about it
>> in this case. I wonder if we should set all randomly for each packet. I don't
>> know what is the better logic here, we can discuss it more in the next version.
> 
> A more sophisticated pkt generator provides various options among
> "step-by-step" / "random" / etc.
> 
> But supporting multiple fields naturally brings this implicitly. It
> won't be a problem as it can be configured by setting the cfg_n_* as
> we discussed above.
> 
> I think rte_rand() is a good option, anyway this can be tweaked easily
> once the framework becomes shaped.
> 

Can be done, but do we really want to add more packet generator capability to
testpmd?

>>
>>>>
>>>>>       }
>>>>>
>>>>>       nb_tx = rte_eth_tx_burst(fs->tx_port, fs->tx_queue, pkts_burst, nb_pkt);
>>>>>       /*
>>>>>        * Retry if necessary
>>>>>        */
>>>>> -     if (unlikely(nb_tx < nb_rx) && fs->retry_enabled) {
>>>>> +     if (unlikely(nb_tx < nb_pkt) && fs->retry_enabled) {
>>>>>               retry = 0;
>>>>> -             while (nb_tx < nb_rx && retry++ < burst_tx_retry_num) {
>>>>> +             while (nb_tx < nb_pkt && retry++ < burst_tx_retry_num) {
>>>>>                       rte_delay_us(burst_tx_delay_time);
>>>>>                       nb_tx += rte_eth_tx_burst(fs->tx_port, fs->tx_queue,
>>>>> -                                     &pkts_burst[nb_tx], nb_rx - nb_tx);
>>>>> +                                     &pkts_burst[nb_tx], nb_pkt - nb_tx);
>>>>>               }
>>>>
>>>> +1 to this fix, thanks for it. But can you please make a seperate patch for
>>>> this, with proper 'Fixes:' tag etc..
>>>
>>> Ok.
>>>
>>>>
>>>>>       }
>>>>> -     fs->tx_packets += nb_tx;
>>>>>
>>>>>       inc_tx_burst_stats(fs, nb_tx);
>>>>> -     if (unlikely(nb_tx < nb_pkt)) {
>>>>> -             /* Back out the flow counter. */
>>>>> -             next_flow -= (nb_pkt - nb_tx);
>>>>> -             while (next_flow < 0)
>>>>> -                     next_flow += cfg_n_flows;
>>>>> +     fs->tx_packets += nb_tx;
>>>>> +     /* Catch up flow idx by actual sent. */
>>>>> +     for (i = 0; i < nb_tx; ++i) {
>>>>> +             RTE_PER_LCORE(_next_udp_dst) = RTE_PER_LCORE(_next_udp_dst) + 1;
>>>>> +             if (RTE_PER_LCORE(_next_udp_dst) < cfg_n_udp_dst)
>>>>> +                     continue;
>>>>> +             RTE_PER_LCORE(_next_udp_dst) = 0;
>>>>> +             RTE_PER_LCORE(_next_udp_src) = RTE_PER_LCORE(_next_udp_src) + 1;
>>>>> +             if (RTE_PER_LCORE(_next_udp_src) < cfg_n_udp_src)
>>>>> +                     continue;
>>>>> +             RTE_PER_LCORE(_next_udp_src) = 0;
>>>>> +             RTE_PER_LCORE(_next_ip_dst) = RTE_PER_LCORE(_next_ip_dst) + 1;
>>>>> +             if (RTE_PER_LCORE(_next_ip_dst) < cfg_n_ip_dst)
>>>>> +                     continue;
>>>>> +             RTE_PER_LCORE(_next_ip_dst) = 0;
>>>>> +             RTE_PER_LCORE(_next_ip_src) = RTE_PER_LCORE(_next_ip_src) + 1;
>>>>> +             if (RTE_PER_LCORE(_next_ip_src) < cfg_n_ip_src)
>>>>> +                     continue;
>>>>> +             RTE_PER_LCORE(_next_ip_src) = 0;
>>>>> +     }
>>>>
>>>> Why per-core variables are not used in forward function, but local variables
>>>> (like 'next_ip_src' etc..) used? Is it for the performance, if so what is the
>>>> impact?
>>>>
>>>> And why not directly assign from local variables to per-core variables, but have
>>>> above catch up loop?
>>>>
>>>>
>>>
>>> Local vars are for generating pkts, global ones catch up finally when
>>> nb_tx is clear.
>>
>> Why you are not using global ones to generate packets? This removes the need for
>> catch up?
> 
> When there are multiple fields, back out the overran index caused by
> dropped packets is not that straightforward -- It's the "carry" issue
> in adding.
> 
>>
>>> So flow indexes only increase by actual sent pkt number.
>>> It serves the same purpose of the original "/* backout the flow counter */".
>>> My math isn't good enough to make it look more intelligent though.
>>>
>>
>> Maybe I am missing something, for this case why not just assign back from locals
>> to globals?
> 
> As above.
> 
> However, this can be simplified if we discard the "back out"
> mechanism: generate 32 pkts and send 20 of them while the rest 12 are
> dropped, the difference is that is the idx gonna start from 21 or 33
> next time?
> 

I am not sure point of "back out", I think we can remove it unless there is no
objection, so receiving end can recognize failed packets.