<div dir="ltr">> Saturate a link in both directions simultaneously with multiple greedy flows while measuring load-dependent latency changes for small isochronous probe flows.<br><div><br></div><div>This functionality is released in iperf 2.1.8 per the bounceback feature but, unfortunately, OpenWRT doesn't maintain iperf 2 as a package anymore and uses 2.0.13 <br><h2 style="color:rgb(0,0,0);font-family:"Times New Roman"">CLIENT SPECIFIC OPTIONS</h2><dl compact style="color:rgb(0,0,0);font-family:"Times New Roman";font-size:medium"><dt><b>--bounceback[=</b><i>n</i><b>]</b></dt><dd>run a TCP bounceback or rps test with optional number writes in a burst per value of n. The default is ten writes every period and the default period is one second (Note: set size with -l or --len which defaults to 100 bytes)</dd><dt><b>--bounceback-congest[=up|down|bidir][</b>,<i>n</i><b>]</b></dt><dd>request a concurrent working load or TCP stream(s), defaults to full duplex (or bidir) unless the <b>up</b> or <b>down</b> option is provided. The number of TCP streams defaults to 1 and can be changed via the n value, e.g. <b>--bounceback-congest=down,4</b> will use four TCP streams from server to the client as the working load. The IP ToS will be BE (0x0) for working load traffic.</dd><dt><b>--bounceback-hold </b><i>n</i></dt><dd>request the server to insert a delay of n milliseconds between its read and write (default is no delay)</dd><dt><b>--bounceback-period[=</b><i>n</i><b>]</b></dt><dd>request the client schedule its send(s) every n seconds (default is one second, use zero value for immediate or continuous back to back)</dd><dt><b>--bounceback-no-quickack</b></dt><dd>request the server not set the TCP_QUICKACK socket option (disabling TCP ACK delays) during a bounceback test (see NOTES)</dd><dt><b>--bounceback-txdelay </b><i>n</i></dt><dd>request the client to delay n seconds between the start of the working load and the bounceback traffic (default is no delay)</dd></dl></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Tue, Oct 11, 2022 at 12:15 AM Sebastian Moeller <<a href="mailto:moeller0@gmx.de">moeller0@gmx.de</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Hi Bob,<br>
<br>
On 11 October 2022 02:05:40 CEST, Bob McMahon <<a href="mailto:bob.mcmahon@broadcom.com" target="_blank">bob.mcmahon@broadcom.com</a>> wrote:<br>
>It's too big because it's oversized so it's in the size domain. It's<br>
>basically Little's law's value for the number of items in a queue.<br>
><br>
>*Number of items in the system = (the rate items enter and leave the<br>
>system) x (the average amount of time items spend in the system)*<br>
><br>
><br>
>Which gets driven to the standing queue size when the arrival rate<br>
>exceeds the service rate - so the driving factor isn't the service and<br>
>arrival rates, but *the queue size *when *any service rate is less than an<br>
>arrival rate.*<br>
<br>
[SM] You could also argue it is the ratio of arrival to service rates, with the queue size being a measure correlating with how long the system will tolerate ratios larger than one...<br>
<br>
<br>
><br>
>In other words, one can find and measure bloat regardless of the<br>
>enter/leave rates (as long as the leave rate is too slow) and the value of<br>
>memory units found will always be the same.<br>
><br>
>Things like prioritizations to jump the line are somewhat of hacks at<br>
>reducing the service time for a specialized class of packets but nobody<br>
>really knows which packets should jump. <br>
<br>
[SM] Au contraire most everybody 'knows' it is their packets that should jump ahead of the rest ;) For intermediate hop queues however that endpoint perception is not really actionable due to lack of robust and reliable importance identifiers on packets. In side a 'domain' dscps might work if treated to strict admission control, but that typically will not help end2end traffic over the internet. This is BTW why I think FQ is a great concept, as it mostly results in the desirable outcome of not picking winners and losers (like arbitrarily starving a flow), but I digress.<br>
<br>
>Also, nobody can define what<br>
>working conditions are so that's another problem with this class of tests.<br>
<br>
[SM] While real working conditions will be different for each link and probably vary over time, it seems achievable to come up with a set of pessimistic assumptions how to model a challenging work condition against which to test potential remedies, assuming that such remedies will also work well under less challenging conditions, no?<br>
<br>
<br>
><br>
>Better maybe just to shrink the queue and eliminate all unneeded queueing<br>
>delays. <br>
<br>
[SM] The 'unneeded' does a lot of work in that sentence ;). I like Van's? Description of queues as shock absorbers so queue size will have a lower acceptable limit assuming users want to achieve 'acceptable' throughput even with existing bursty senders. (Not all applications are suited for pacing so some level of burstiness seems unavoidable).<br>
<br>
<br>
> Also, measure the performance per "user conditions" which is going<br>
>to be different for almost every environment (and is correlated to time and<br>
>space.) So any engineering solution is fundamentally suboptimal. <br>
<br>
[SM] A matter of definition, if the requirement is to cover many user conditions the optimality measure simply needs to be changed from per individual condition to over many/all conditions, no?<br>
<br>
>Even<br>
>pacing the source doesn't necessarily do the right thing because that's<br>
>like waiting in the waitlist while at home vs the restaurant lobby. <br>
<br>
[SM] +1.<br>
<br>
> Few<br>
>care about where messages wait (unless the pitch is AQM is the only<br>
>solution that drives to a self-fulfilling prophecy - that's why the tests<br>
>have to come up with artificial conditions that can't be simply defined.)<br>
<br>
Hrm, so the RRUL test, while not the end all of bufferbloat/working conditions tests, is not that complicated:<br>
Saturate a link in both directions simultaneously with multiple greedy flows while measuring load-dependent latency changes for small isochronous probe flows.<br>
<br>
Yes, the it would be nice to have additional higher rate probe flows also bursty ones to emulate on-linev games, and 'pumped' greedy flows to emulate DASH 'streaming', and a horde of small greedy flows that mostly end inside the initial window and slow start. But at its core existing RRUL already gives a useful estimate on how a link behaves under saturating loads all the while being relatively simple.<br>
The responsiveness under working condition seems similar in that it tries to saturate a link with an increasing number of greedy flows, in a sense to create a reasonable bad case that ideally rarely happens.<br>
<br>
Regards<br>
Sebastian<br>
<br>
<br>
><br>
>Bob<br>
><br>
>On Mon, Oct 10, 2022 at 3:57 PM David Lang <<a href="mailto:david@lang.hm" target="_blank">david@lang.hm</a>> wrote:<br>
><br>
>> On Mon, 10 Oct 2022, Bob McMahon via Bloat wrote:<br>
>><br>
>> > I think conflating bufferbloat with latency misses the subtle point in<br>
>> that<br>
>> > bufferbloat is a measurement in memory units more than a measurement in<br>
>> > time units. The first design flaw is a queue that is too big. This<br>
>> youtube<br>
>> > video analogy doesn't help one understand this important point.<br>
>><br>
>> but the queue is only too big because of the time it takes to empty the<br>
>> queue,<br>
>> which puts us back into the time domain.<br>
>><br>
>> David Lang<br>
>><br>
>> > Another subtle point is that the video assumes AQM as the only solution<br>
>> and<br>
>> > ignores others, i.e. pacing at the source(s) and/or faster service<br>
>> rates. A<br>
>> > restaurant that let's one call ahead to put their name on the waitlist<br>
>> > doesn't change the wait time. Just because a transport layer slowed down<br>
>> > and hasn't congested a downstream queue doesn't mean the e2e latency<br>
>> > performance will meet the gaming needs as an example. The delay is still<br>
>> > there it's just not manifesting itself in a shared queue that may or may<br>
>> > not negatively impact others using that shared queue.<br>
>> ><br>
>> > Bob<br>
>> ><br>
>> ><br>
>> ><br>
>> > On Mon, Oct 10, 2022 at 2:40 AM Sebastian Moeller via Make-wifi-fast <<br>
>> > <a href="mailto:make-wifi-fast@lists.bufferbloat.net" target="_blank">make-wifi-fast@lists.bufferbloat.net</a>> wrote:<br>
>> ><br>
>> >> Hi Erik,<br>
>> >><br>
>> >><br>
>> >>> On Oct 10, 2022, at 11:32, Taraldsen Erik <<a href="mailto:erik.taraldsen@telenor.no" target="_blank">erik.taraldsen@telenor.no</a>><br>
>> >> wrote:<br>
>> >>><br>
>> >>> On 10/10/2022, 11:09, "Sebastian Moeller" <<a href="mailto:moeller0@gmx.de" target="_blank">moeller0@gmx.de</a>> wrote:<br>
>> >>><br>
>> >>> Nice!<br>
>> >>><br>
>> >>>> On Oct 10, 2022, at 07:52, Taraldsen Erik via Cake <<br>
>> >> <a href="mailto:cake@lists.bufferbloat.net" target="_blank">cake@lists.bufferbloat.net</a>> wrote:<br>
>> >>>><br>
>> >>>> It took about 3 hours from the video was release before we got the<br>
>> >> first request to have SQM on the CPE's we manage as a ISP. Finally<br>
>> >> getting some customer response on the issue.<br>
>> >>><br>
>> >>> [SM] Will you be able to bump these requests to higher-ups and at<br>
>> >> least change some perception of customer demand for tighter latency<br>
>> >> performance?<br>
>> >>><br>
>> >>> That would be the hope.<br>
>> >><br>
>> >> [SM} Excellent, hope this plays out as we wish for.<br>
>> >><br>
>> >><br>
>> >>> We actually have fq_codel implemented on the two latest generations of<br>
>> >> DSL routers. Use sync rate as input to set the rate. Works quite well.<br>
>> >><br>
>> >> [SM] Cool, if I might ask what fraction of the sync are you<br>
>> >> setting the traffic shaper for and are you doing fine grained overhead<br>
>> >> accounting (or simply fold that into a grand "de-rating"-factor)?<br>
>> >><br>
>> >><br>
>> >>> There is also a bit of traction around <a href="http://speedtest.net" rel="noreferrer" target="_blank">speedtest.net</a>'s inclusion of<br>
>> >> latency under load internally.<br>
>> >><br>
>> >> [SM] Yes, although IIUC they are reporting the interquartile<br>
>> mean<br>
>> >> for the two loaded latency estimates, which is pretty conservative and<br>
>> only<br>
>> >> really "triggers" for massive consistently elevated latency; so I expect<br>
>> >> this to be great for detecting really bad cases, but I fear it is too<br>
>> >> conservative and will make a number of problematic links look OK. But<br>
>> hey,<br>
>> >> even that is leaps and bounds better than the old only idle latency<br>
>> report.<br>
>> >><br>
>> >><br>
>> >>> My hope is that some publication in Norway will pick up on that score<br>
>> >> and do a test and get some mainstream publicity with the results.<br>
>> >><br>
>> >> [SM] Inside the EU the challenge is to get national regulators<br>
>> and<br>
>> >> the BEREC to start bothering about latency-under-load at all, "some<br>
>> >> mainstream publicity" would probably help here as well.<br>
>> >><br>
>> >> Regards<br>
>> >> Sebastian<br>
>> >><br>
>> >><br>
>> >>><br>
>> >>> -Erik<br>
>> >>><br>
>> >>><br>
>> >>><br>
>> >><br>
>> >> _______________________________________________<br>
>> >> Make-wifi-fast mailing list<br>
>> >> <a href="mailto:Make-wifi-fast@lists.bufferbloat.net" target="_blank">Make-wifi-fast@lists.bufferbloat.net</a><br>
>> >> <a href="https://lists.bufferbloat.net/listinfo/make-wifi-fast" rel="noreferrer" target="_blank">https://lists.bufferbloat.net/listinfo/make-wifi-fast</a><br>
>> ><br>
>> >_______________________________________________<br>
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>><br>
><br>
<br>
-- <br>
Sent from my Android device with K-9 Mail. Please excuse my brevity.<br>
</blockquote></div>
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