netdev - Re: [PATCH net-next v3] Add Common Applications Kept Enhanced (cake) qdisc

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Date:   Wed, 25 Apr 2018 09:29:03 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Toke Høiland-Jørgensen <toke@...e.dk>,
        Eric Dumazet <eric.dumazet@...il.com>, netdev@...r.kernel.org
Cc:     cake@...ts.bufferbloat.net, Dave Taht <dave.taht@...il.com>
Subject: Re: [PATCH net-next v3] Add Common Applications Kept Enhanced (cake)
 qdisc



On 04/25/2018 09:06 AM, Toke Høiland-Jørgensen wrote:
> Eric Dumazet <eric.dumazet@...il.com> writes:
> 
>> On 04/25/2018 08:22 AM, Toke Høiland-Jørgensen wrote:
>>> Eric Dumazet <eric.dumazet@...il.com> writes:
>>
>>>> What performance number do you get on a 10Gbit NIC for example ?
>>>
>>> Single-flow throughput through 2 hops on a 40Gbit connection (with CAKE
>>> in unlimited mode vs pfifo_fast on the router):
>>>
>>> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to testbed-40g-2 () port 0 AF_INET : demo
>>> Recv   Send    Send                          
>>> Socket Socket  Message  Elapsed              
>>> Size   Size    Size     Time     Throughput  
>>> bytes  bytes   bytes    secs.    10^6bits/sec  
>>>
>>>  87380  16384  16384    10.00    18840.40   
>>>
>>> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to testbed-40g-2 () port 0 AF_INET : demo
>>> Recv   Send    Send                          
>>> Socket Socket  Message  Elapsed              
>>> Size   Size    Size     Time     Throughput  
>>> bytes  bytes   bytes    secs.    10^6bits/sec  
>>>
>>>  87380  16384  16384    10.00    24804.77   
>>
>> CPU performance would be interesting here.  (netperf -Cc)
> 
> 
> $ sudo tc qdisc replace dev ens2 root cake
> $ netperf -cC -H 10.70.2.2
> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.70.2.2 () port 0 AF_INET : demo
> Recv   Send    Send                          Utilization       Service Demand
> Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
> Size   Size    Size     Time     Throughput  local    remote   local   remote
> bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB
> 
>  87380  16384  16384    10.00      15450.35   13.35    6.68     0.849   0.283  
> 
> $ sudo tc qdisc del dev ens2 root 
> $ netperf -cC -H 10.70.2.2
> MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 10.70.2.2 () port 0 AF_INET : demo
> Recv   Send    Send                          Utilization       Service Demand
> Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
> Size   Size    Size     Time     Throughput  local    remote   local   remote
> bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB
> 
>  87380  16384  16384    10.00      36414.23   8.20     14.30    0.221   0.257  
> 
> 
> (In this test I'm running netperf on the machine that was a router
> before, which is why the base throughput is higher; the other machine
> runs out of CPU on the sender side).

We can see here the high cost of forcing software GSO :/

Really, this should be done only :
1) If requested by the admin ( tc .... gso ....)

2) If packet size is above a threshold.
  The threshold could be set by the admin, and/or based on a fraction of the bandwidth parameter.

I totally understand why you prefer to segment yourself for < 100 Mbit links.

But this makes no sense on 10Gbit+