[Bloat] Little's Law mea culpa, but not invalidating my main point

Bob McMahon bob.mcmahon at broadcom.com
Mon Jul 12 14:38:24 EDT 2021

To be clear, it's a OS write() using a socket opened with TCP and the final
OS read() of that write. The write size is set using -l or --length. OWD
requires --trip-times option.


On Mon, Jul 12, 2021 at 11:21 AM Bob McMahon <bob.mcmahon at broadcom.com>

> iperf 2 supports OWD and gives full histograms for TCP write to read, TCP
> connect times, latency of packets (with UDP), latency of "frames" with
> simulated video traffic (TCP and UDP), xfer times of bursts with low duty
> cycle traffic, and TCP RTT (sampling based.) It also has support for
> sampling (per interval reports) down to 100 usecs if configured with
> --enable-fastsampling, otherwise the fastest sampling is 5 ms. We've
> released all this as open source.
> OWD only works if the end realtime clocks are synchronized using a
> "machine level" protocol such as IEEE 1588 or PTP. Sadly, *most data
> centers don't provide sufficient level of clock accuracy and the GPS pulse
> per second * to colo and vm customers.
> https://iperf2.sourceforge.io/iperf-manpage.html
> Bob
> On Mon, Jul 12, 2021 at 10:40 AM David P. Reed <dpreed at deepplum.com>
> wrote:
>> On Monday, July 12, 2021 9:46am, "Livingood, Jason" <
>> Jason_Livingood at comcast.com> said:
>> > I think latency/delay is becoming seen to be as important certainly, if
>> not a more direct proxy for end user QoE. This is all still evolving and I
>> have to say is a super interesting & fun thing to work on. :-)
>> If I could manage to sell one idea to the management hierarchy of
>> communications industry CEOs (operators, vendors, ...) it is this one:
>> "It's the end-to-end latency, stupid!"
>> And I mean, by end-to-end, latency to complete a task at a relevant layer
>> of abstraction.
>> At the link level, it's packet send to packet receive completion.
>> But at the transport level including retransmission buffers, it's
>> datagram (or message) origination until the acknowledgement arrives for
>> that message being delivered after whatever number of retransmissions,
>> freeing the retransmission buffer.
>> At the WWW level, it's mouse click to display update corresponding to
>> completion of the request.
>> What should be noted is that lower level latencies don't directly predict
>> the magnitude of higher-level latencies. But longer lower level latencies
>> almost always amplfify higher level latencies. Often non-linearly.
>> Throughput is very, very weakly related to these latencies, in contrast.
>> The amplification process has to do with the presence of queueing.
>> Queueing is ALWAYS bad for latency, and throughput only helps if it is in
>> exactly the right place (the so-called input queue of the bottleneck
>> process, which is often a link, but not always).
>> Can we get that slogan into Harvard Business Review? Can we get it taught
>> in Managerial Accounting at HBS? (which does address logistics/supply chain
>> queueing).

This electronic communication and the information and any files transmitted 
with it, or attached to it, are confidential and are intended solely for 
the use of the individual or entity to whom it is addressed and may contain 
information that is confidential, legally privileged, protected by privacy 
laws, or otherwise restricted from disclosure to anyone else. If you are 
not the intended recipient or the person responsible for delivering the 
e-mail to the intended recipient, you are hereby notified that any use, 
copying, distributing, dissemination, forwarding, printing, or copying of 
this e-mail is strictly prohibited. If you received this e-mail in error, 
please return the e-mail to the sender, delete it from your computer, and 
destroy any printed copy of it.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.bufferbloat.net/pipermail/cerowrt-devel/attachments/20210712/12e186df/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/pkcs7-signature
Size: 4206 bytes
Desc: S/MIME Cryptographic Signature
URL: <https://lists.bufferbloat.net/pipermail/cerowrt-devel/attachments/20210712/12e186df/attachment-0001.bin>

More information about the Cerowrt-devel mailing list