[e2e] Historical question: Link layer flow control / silent discard
anoop at alumni.duke.edu
Sun May 26 13:48:37 PDT 2013
On Sun, May 26, 2013 at 9:50 AM, Matt Mathis <mattmathis at google.com> wrote:
> As for link layer flow control, it doesn't work. You can buy it today in
> many technologies, but if you turn it on, you will rediscover head-of-line
> blocking and global resource contention. e.g. If you have one overloaded
> exit, the cascaded backlogs at each stage through the fabric guarantee
> congestion and/or resource starvation everywhere, even if the rest of the
> fabric is otherwise lightly loaded.
> I don't know that I would say that LLFC doesn't work. It works for what
is it designed to do...operate within usec to very-short term congestion to
guarantee a near lossless link network. It is definitely not designed to
handle sustained overloads...end-to-end flow control works best there.
This presentations discusses some of these issues on slides 16-23.
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