[Cerowrt-devel] Problems testing sqm

[David P. Reed]

Not trying to haggle. Just pointing out that this test configuration has a very short RTT. maybe too short for our SQM to adjust to.

On Oct 24, 2015, Sebastian Moeller <moeller0 at gmx.de> wrote:
>Hi David,
>
>On Oct 24, 2015, at 00:53 , David P. Reed <dpreed at reed.com> wrote:
>
>> In particular,  the DUT should probably have no more than 2 packets
>of outbound queueing given the very small RTT. 2xRTT is the most
>buffering you want in the loop.
>
>	Let’s not haggle about the precise amount of queueing we deem
>acceptable, as long as we all agree that >= 2 seconds is simply not
>acceptable ;) (the default sqm will approximately limit the latency
>under load increase (LULI) to roughly twice the target or typically 10
>ms; note that this LULI only applies to unrelated flows). The exact
>number of queued packets seems to correlate with the beefiness of the
>DUT, the beefier the fewer packets should work, wimpier devices might
>need to batch some processing up, resulting in  higher LULI…
>
>Best Regards
>	Sebastian
>
>> 
>> On Oct 23, 2015, Richard Smith <smithbone at gmail.com> wrote:
>> On 10/23/2015 02:41 PM, Michael Richardson wrote:
>> Richard Smith <smithbone at gmail.com> wrote:
>> My test setup:
>> 
>> Laptop<--1000BaseT-->DUT<--1000baseT-->Server
>> 
>> So, given that the DUT is the only real constraint in the network,
>what
>> do you expect to see from this setup?
>> 
>> Given that the probably DUT can't forward at Gb/s, and it certainly
>can't
>> shape anything, it's gonna drop packets, and it's probably gonna drop
>them in
>> Rx, having overrun the Rx-queue (so tail-drop). If there is too much
>ram
>> (bufferbloated), then you'll see different results...
>> 
>> Setting ingress/egress to 10Mbit/s I expected to see the speed 
>> measurements bounce around those limits with the ping times staying
>in 
>> the low double digits of ms. What I saw however, was the data rates 
>> going well past 10Mbit limit and pings up to 2000 ms.
>> 
>> This is what I've seen in prior rrul testing using a the 50/10 cable 
>> link at our office and my 25(ish)/6 link at my apartment and a well 
>> connected server on the net. That however was using QoS and not SQM.
>> 
>> Its that a reasonable expectation?
>> 
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