[Cerowrt-devel] Problems testing sqm

Sebastian Moeller moeller0 at gmx.de
Sat Oct 24 04:07:18 EDT 2015

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

> 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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