[e2e] Historical question: Link layer flow control / silent discard

[Anoop Ghanwani]

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.
http://www.c3.lanl.gov/cac2007/presentations/hendel.pdf

Anoop
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