[Bloat] [Make-wifi-fast] [Cake] The most wonderful video ever about bufferbloat

Tue Oct 11 12:58:05 EDT 2022

> Saturate a link in both directions simultaneously with multiple greedy
flows while measuring load-dependent latency changes for small isochronous
probe flows.

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
CLIENT SPECIFIC OPTIONS*--bounceback[=**n**]*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)
*--bounceback-congest[=up|down|bidir][*,*n**]*request a concurrent working
load or TCP stream(s), defaults to full duplex (or bidir) unless the *up*
 or *down* option is provided. The number of TCP streams defaults to 1 and
can be changed via the n value, e.g. *--bounceback-congest=down,4* 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.*--bounceback-hold **n*request
the server to insert a delay of n milliseconds between its read and write
(default is no delay)*--bounceback-period[=**n**]*request the client
schedule its send(s) every n seconds (default is one second, use zero value
for immediate or continuous back to back)*--bounceback-no-quickack*request
the server not set the TCP_QUICKACK socket option (disabling TCP ACK
delays) during a bounceback test (see NOTES)*--bounceback-txdelay **n*request
the client to delay n seconds between the start of the working load and the
bounceback traffic (default is no delay)

On Tue, Oct 11, 2022 at 12:15 AM Sebastian Moeller <moeller0 at gmx.de> wrote:

> Hi Bob,
>
> On 11 October 2022 02:05:40 CEST, Bob McMahon <bob.mcmahon at broadcom.com>
> wrote:
> >It's too big because it's oversized so it's in the size domain. It's
> >basically Little's law's value for the number of items in a queue.
> >
> >*Number of items in the system = (the rate items enter and leave the
> >system) x (the average amount of time items spend in the system)*
> >
> >
> >Which gets driven to the standing queue size when the arrival rate
> >exceeds the service rate - so the driving factor isn't the service and
> >arrival rates, but *the queue size *when *any service rate is less than an
> >arrival rate.*
>
> [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...
>
>
> >
> >In other words, one can find and measure bloat regardless of the
> >enter/leave rates (as long as the leave rate is too slow) and the value of
> >memory units found will always be the same.
> >
> >Things like prioritizations to jump the line are somewhat of hacks at
> >reducing the service time for a specialized class of packets but nobody
> >really knows which packets should jump.
>
> [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.
>
> >Also, nobody can define what
> >working conditions are so that's another problem with this class of tests.
>
> [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?
>
>
> >
> >Better maybe just to shrink the queue and eliminate all unneeded queueing
> >delays.
>
> [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).
>
>
> > Also, measure the performance per "user conditions" which is going
> >to be different for almost every environment (and is correlated to time
> and
> >space.) So any engineering solution is fundamentally suboptimal.
>
> [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?
>
> >Even
> >pacing the source doesn't necessarily do the right thing because that's
> >like waiting in the waitlist while at home vs the restaurant lobby.
>
> [SM] +1.
>
> > Few
> >care about where messages wait (unless the pitch is AQM is the only
> >solution that drives to a self-fulfilling prophecy - that's why the tests
> >have to come up with artificial conditions that can't be simply defined.)
>
> Hrm, so the RRUL test, while not the end all of bufferbloat/working
> conditions tests, is not that complicated:
> Saturate a link in both directions simultaneously with multiple greedy
> flows while measuring load-dependent latency changes for small isochronous
> probe flows.
>
> 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.
> 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.
>
> Regards
>       Sebastian
>
>
> >
> >Bob
> >
> >On Mon, Oct 10, 2022 at 3:57 PM David Lang <david at lang.hm> wrote:
> >
> >> On Mon, 10 Oct 2022, Bob McMahon via Bloat wrote:
> >>
> >> > I think conflating bufferbloat with latency misses the subtle point in
> >> that
> >> > bufferbloat is a measurement in memory units more than a measurement
> in
> >> > time units. The first design flaw is a queue that is too big. This
> >> youtube
> >> > video analogy doesn't help one understand this important point.
> >>
> >> but the queue is only too big because of the time it takes to empty the
> >> queue,
> >> which puts us back into the time domain.
> >>
> >> David Lang
> >>
> >> > Another subtle point is that the video assumes AQM as the only
> solution
> >> and
> >> > ignores others, i.e. pacing at the source(s) and/or faster service
> >> rates. A
> >> > restaurant that let's one call ahead to put their name on the waitlist
> >> > doesn't change the wait time. Just because a transport layer slowed
> down
> >> > and hasn't congested a downstream queue doesn't mean the e2e latency
> >> > performance will meet the gaming needs as an example. The delay is
> still
> >> > there it's just not manifesting itself in a shared queue that may or
> may
> >> > not negatively impact others using that shared queue.
> >> >
> >> > Bob
> >> >
> >> >
> >> >
> >> > On Mon, Oct 10, 2022 at 2:40 AM Sebastian Moeller via Make-wifi-fast <
> >> > make-wifi-fast at lists.bufferbloat.net> wrote:
> >> >
> >> >> Hi Erik,
> >> >>
> >> >>
> >> >>> On Oct 10, 2022, at 11:32, Taraldsen Erik <
> erik.taraldsen at telenor.no>
> >> >> wrote:
> >> >>>
> >> >>> On 10/10/2022, 11:09, "Sebastian Moeller" <moeller0 at gmx.de> wrote:
> >> >>>
> >> >>>    Nice!
> >> >>>
> >> >>>> On Oct 10, 2022, at 07:52, Taraldsen Erik via Cake <
> >> >> cake at lists.bufferbloat.net> wrote:
> >> >>>>
> >> >>>> It took about 3 hours from the video was release before we got the
> >> >> first request to have SQM on the CPE's  we manage as a ISP.  Finally
> >> >> getting some customer response on the issue.
> >> >>>
> >> >>>       [SM] Will you be able to bump these requests to higher-ups
> and at
> >> >> least change some perception of customer demand for tighter latency
> >> >> performance?
> >> >>>
> >> >>> That would be the hope.
> >> >>
> >> >>         [SM} Excellent, hope this plays out as we wish for.
> >> >>
> >> >>
> >> >>>  We actually have fq_codel implemented on the two latest
> generations of
> >> >> DSL routers.  Use sync rate as input to set the rate.  Works quite
> well.
> >> >>
> >> >>         [SM] Cool, if I might ask what fraction of the sync are you
> >> >> setting the traffic shaper for and are you doing fine grained
> overhead
> >> >> accounting (or simply fold that into a grand "de-rating"-factor)?
> >> >>
> >> >>
> >> >>> There is also a bit of traction around speedtest.net's inclusion of
> >> >> latency under load internally.
> >> >>
> >> >>         [SM] Yes, although IIUC they are reporting the interquartile
> >> mean
> >> >> for the two loaded latency estimates, which is pretty conservative
> and
> >> only
> >> >> really "triggers" for massive consistently elevated latency; so I
> expect
> >> >> this to be great for detecting really bad cases, but I fear it is too
> >> >> conservative and will make a number of problematic links look OK. But
> >> hey,
> >> >> even that is leaps and bounds better than the old only idle latency
> >> report.
> >> >>
> >> >>
> >> >>> My hope is that some publication in Norway will pick up on that
> score
> >> >> and do a test and get some mainstream publicity with the results.
> >> >>
> >> >>         [SM] Inside the EU the challenge is to get national
> regulators
> >> and
> >> >> the BEREC to start bothering about latency-under-load at all, "some
> >> >> mainstream publicity" would probably help here as well.
> >> >>
> >> >> Regards
> >> >>         Sebastian
> >> >>
> >> >>
> >> >>>
> >> >>> -Erik
> >> >>>
> >> >>>
> >> >>>
> >> >>
> >> >> _______________________________________________
> >> >> Make-wifi-fast mailing list
> >> >> Make-wifi-fast at lists.bufferbloat.net
> >> >> https://lists.bufferbloat.net/listinfo/make-wifi-fast
> >> >
> >> >_______________________________________________
> >> Bloat mailing list
> >> Bloat at lists.bufferbloat.net
> >> https://lists.bufferbloat.net/listinfo/bloat
> >>
> >
>
> --
> Sent from my Android device with K-9 Mail. Please excuse my brevity.
>

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