On Mon, 3 Apr 2023, Ayush Mishra via Bloat wrote:
==> I agree too. But I think one of the key challenges here could be when
the dynamically entering flows are extremely tiny (which I imagine is quite
common). In those cases, there is a possibility that by the time the
long-running flow backs off, the congestion it was responding to has
already ended because the tiny flows have exited the bottleneck (think
microbursts caused by flows that last 1-2 RTTs). In a perfect world we'd
like to deal with elephant and mice flows in isolation at the switch, but
there are likely things we can do from the endpoint too. Maybe some kind of
a two-phase backoff, with the second phase only kicking in after a period
of hysteresis to make sure it's responding to persistent congestion and not
just brief microbursts. This is just off the top of my head, so I'm not
sure how something like this would play out in the overall dynamics and
convergence of the algorithm that implements it.
if the backoff is less drastic than currently, I would say that it's reasonable
to have the elephant back off for congestion caused by a microburst, as such
bursts are not uncommon, and while the one that triggered the backoff may finish
before the backoff happens, it's made room for the next one.
David Lang
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