On Mon, 5 Apr 2021, Stephen Hemminger wrote:
On Mon, 5 Apr 2021 08:46:15 -0400
Rich Brown <[email protected]> wrote:
Dave Täht has put me up to revising the current Bufferbloat article on
Wikipedia (https://en.wikipedia.org/wiki/Bufferbloat)
Before I get into it, I want to ask real experts for some guidance... Here goes:
1) What is *our* definition of Bufferbloat? (We invented the term, so I think we get to define it.)
a) Are we content with the definition from the bufferbloat.net site, "Bufferbloat is
the undesirable latency that comes from a router or other network equipment buffering too
much data." (This suggests bufferbloat is latency, and could be measured in
seconds/msec.)
b) Or should we use something like Jim Gettys' definition from the Dark Buffers article (https://ieeexplore.ieee.org/document/5755608), "Bufferbloat is the existence of excessively large (bloated) buffers in systems, particularly network communication systems." (This suggests bufferbloat is an unfortunate state of nature, measured in units of "unhappiness" :-)
c) Or some other definition?
2) All network equipment can be bloated. I have seen (but not really followed)
controversy regarding the amount of buffering needed in the Data Center. Is it worth
having the Wikipedia article distinguish between Data Center equipment and CPE/home/last
mile equipment? Similarly, is the "bloat condition" and its mitigation
qualitatively different between those applications? Finally, do any of us know how
frequently data centers/backbone ISPs experience buffer-induced latencies? What's the
magnitude of the impact?
3) The Wikipedia article mentions guidance that network gear should accommodate buffering
250 msec of traffic(!) Is this a real "rule of thumb" or just an often-repeated
but unscientific suggestion? Can someone give pointers to best practices?
4) Meta question: Can anyone offer any advice on making a wholesale change to a
Wikipedia article? Before I offer a fork-lift replacement I would a) solicit
advice on the new text from this list, and b) try to make contact with some of
the reviewers and editors who've been maintaining the page to establish some
bona fides and rapport...
Many thanks!
Rich
I like to think of Bufferbloat as a combination of large buffers and how
algorithms react to those buffers.
I think there are two things
1. what bufferbloat is
bufferbloat is the result of memory getting cheaper faster than bandwidth
increased, combined with throughput benchmarking that drastically penalized
end-to-end retries.
I think this definition is pretty academic and not something to worry about
using.
2. why it's a problem
the problems show up when the buffer represents too much time worth of data to
transmit (the time between when the last byte in the buffer gets inserted into
the buffer and when it gets transmitted)
So in a high bandwidth environment (like a datacenter) you can use much larger
buffers than when you are on a low bandwidth line
David Lang
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