Re: [PATCH RFC net-next 1/2] net: Reference bpf_redirect_info via task_struct on PREEMPT_RT.

[Jesper Dangaard Brouer <hawk@kernel.org>]

On 20/02/2024 13.08, Sebastian Andrzej Siewior wrote:
> On 2024-02-20 11:42:57 [+0100], Jesper Dangaard Brouer wrote:
>> This seems low...
>> Have you remembered to disable Ethernet flow-control?
> 
> No but one side says:
> | i40e 0000:3d:00.1 eno2np1: NIC Link is Up, 10 Gbps Full Duplex, Flow Control: None
> 
> but I did this
> 
>>   # ethtool -A ixgbe1 rx off tx off
>>   # ethtool -A i40e2 rx off tx off
> 
> and it didn't change much.
> 
>>
>>> | Summary                 8,436,294 rx/s                  0 err/s
>>
>> You want to see the "extended" info via cmdline (or Ctrl+\)
>>
>>   # xdp-bench drop -e eth1
>>
>>
>>>
>>> with "-t 8 -b 64". I started with 2 and then increased until rx/s was
>>> falling again. I have ixgbe on the sending side and i40e on the
>>
>> With ixgbe on the sending side, my testlab shows I need -t 2.
>>
>> With -t 2 :
>> Summary                14,678,170 rx/s                  0 err/s
>>    receive total        14,678,170 pkt/s        14,678,170 drop/s         0
>> error/s
>>      cpu:1              14,678,170 pkt/s        14,678,170 drop/s         0
>> error/s
>>    xdp_exception                 0 hit/s
>>
>> with -t 4:
>>
>> Summary                10,255,385 rx/s                  0 err/s
>>    receive total        10,255,385 pkt/s        10,255,385 drop/s         0
>> error/s
>>      cpu:1              10,255,385 pkt/s        10,255,385 drop/s         0
>> error/s
>>    xdp_exception                 0 hit/s
>>
>>> receiving side. I tried to receive on ixgbe but this ended with -ENOMEM
>>> | # xdp-bench drop eth1
>>> | Failed to attach XDP program: Cannot allocate memory
>>>
>>> This is v6.8-rc5 on both sides. Let me see where this is coming from…
>>>
>>
>> Another pitfall with ixgbe is that it does a full link reset when
>> adding/removing XDP prog on device.  This can be annoying if connected
>> back-to-back, because "remote" pktgen will stop on link reset.
> 
> so I replaced nr_cpu_ids with 64 and bootet maxcpus=64 so that I can run
> xdp-bench on the ixgbe.
> 

Yes, ixgbe HW have limited TX queues, and XDP tries to allocate a
hardware TX queue for every CPU in the system.  So, I guess you have too
many CPUs in your system - lol.

Other drivers have a fallback to a locked XDP TX path, so this is also
something to lookout for in the machine with i40e.

> so. i40 send, ixgbe receive.
> 
> -t 2
> 
> | Summary                 2,348,800 rx/s                  0 err/s
> |   receive total         2,348,800 pkt/s         2,348,800 drop/s                0 error/s
> |     cpu:0               2,348,800 pkt/s         2,348,800 drop/s                0 error/s
> |   xdp_exception                 0 hit/s
>

This is way too low, with i40e sending.

On my system with only -t 1 my i40e driver can send with approx 15Mpps:

  Ethtool(i40e2) stat:  15028585 (  15,028,585) <= tx-0.packets /sec
  Ethtool(i40e2) stat:  15028589 (  15,028,589) <= tx_packets /sec


> -t 4
> | Summary                 4,158,199 rx/s                  0 err/s
> |   receive total         4,158,199 pkt/s         4,158,199 drop/s                0 error/s
> |     cpu:0               4,158,199 pkt/s         4,158,199 drop/s                0 error/s
> |   xdp_exception                 0 hit/s
> 

Do notice that this is all hitting CPU:0
(this is by design from pktgen_sample03_burst_single_flow.sh)


> -t 8
> | Summary                 5,612,861 rx/s                  0 err/s
> |   receive total         5,612,861 pkt/s         5,612,861 drop/s                0 error/s
> |     cpu:0               5,612,861 pkt/s         5,612,861 drop/s                0 error/s
> |   xdp_exception                 0 hit/s
> 
> going higher makes the rate drop. With 8 it floats between 5,5… 5,7…
> 

At -t 8 we seem to have hit limit on RX side, which also seems too low.

I recommend checking what speeds packet generator is sending with.
I use this tool: ethtool_stats.pl
 
https://github.com/netoptimizer/network-testing/blob/master/bin/ethtool_stats.pl

What we are basically asking: Make sure packet generator is not the
limiting factor in your tests.
As we need to make sure DUT (Device Under Test) is being overloaded
100%.  I often also check (via per record) that DUT don't have idle CPU
cycles (yes, this can easily happen... and happens when we hit a limit
in hardware either NIC or PCIe slot)


> Doing "ethtool -G eno2np1 tx 4096 rx 4096" on the i40 makes it worse,
> using the default 512/512 gets the numbers from above, going below 256
> makes it worse.
> 
> receiving on i40, sending on ixgbe:
> 
> -t 2
> |Summary                 3,042,957 rx/s                  0 err/s
> |  receive total         3,042,957 pkt/s         3,042,957 drop/s                0 error/s
> |    cpu:60              3,042,957 pkt/s         3,042,957 drop/s                0 error/s
> |  xdp_exception                 0 hit/s
> 
> -t 4
> |Summary                 5,442,166 rx/s                  0 err/s
> |  receive total         5,442,166 pkt/s         5,442,166 drop/s                0 error/s
> |    cpu:60              5,442,166 pkt/s         5,442,166 drop/s                0 error/s
> |  xdp_exception                 0 hit/s
> 
> 
> -t 6
> | Summary                 7,023,406 rx/s                  0 err/s
> |   receive total         7,023,406 pkt/s         7,023,406 drop/s                0 error/s
> |     cpu:60              7,023,406 pkt/s         7,023,406 drop/s                0 error/s
> |   xdp_exception                 0 hit/s
> 
> 
> -t 8
> | Summary                 7,540,915 rx/s                  0 err/s
> |   receive total         7,540,915 pkt/s         7,540,915 drop/s                0 error/s
> |     cpu:60              7,540,915 pkt/s         7,540,915 drop/s                0 error/s
> |   xdp_exception                 0 hit/s
> 
> -t 10
> |Summary                 7,699,143 rx/s                  0 err/s
> |  receive total         7,699,143 pkt/s         7,699,143 drop/s                0 error/s
> |    cpu:60              7,699,143 pkt/s         7,699,143 drop/s                0 error/s
> |  xdp_exception                 0 hit/s
> 

At this level, if you can verify that CPU:60 is 100% loaded, and packet
generator is sending more than rx number, then it could work as a valid
experiment.

> -t 18
> | Summary                 7,784,946 rx/s                  0 err/s
> |   receive total         7,784,946 pkt/s         7,784,946 drop/s                0 error/s
> |     cpu:60              7,784,946 pkt/s         7,784,946 drop/s                0 error/s
> |   xdp_exception                 0 hit/s
> 
> after t18 it drop down to 2,…
> Now I got worse than before since -t8 says 7,5… and it did 8,4 in the
> morning. Do you have maybe a .config for me in case I did not enable the
> performance switch?
> 

I would look for root-cause with perf record +
  perf report --sort cpu,comm,dso,symbol --no-children


--Jesper