Re: Deadlocking in the transport

Mikkel Fahnøe Jørgensen <mikkelfj@gmail.com> Wed, 10 January 2018 20:40 UTC

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Subject: Re: Deadlocking in the transport
To: "Charles 'Buck' Krasic" <ckrasic@google.com>, Jana Iyengar <jri@google.com>, QUIC WG <quic@ietf.org>, Martin Thomson <martin.thomson@gmail.com>
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How about a reserve bandwidth function in the API. Header transport could
reserve the minimum needed to ensure a deadlock, and another reserve for
the general traffic. This isolates bandwith consumption from other streams.

I hinted at this earlier. Just like you can share to the total bandwidth
across streams, you can share bandwidth across resource groups, where each
stream belongs to a resource group.

You can provide priorities to groups, but that should not mean the highest
priority takes all. It would be inconvenient and could lead to other
deadlocks. Deficit Round Robin can be applied to groups.

https://en.wikipedia.org/wiki/Deficit_round_robin

Kind Regards,
Mikkel Fahnøe Jørgensen


On 10 January 2018 at 21.32.25, Jana Iyengar (jri@google.com) wrote:

On Wed, Jan 10, 2018 at 12:23 PM, Dmitri Tikhonov <
dtikhonov@litespeedtech.com>; wrote:

> On Wed, Jan 10, 2018 at 12:14:13PM -0800, Jana Iyengar wrote:
> > SHOULD is pretty strong. It's not a guarantee, but then a transport
> > implementation that doesn't do it is expected to know what it's doing.
>
> If an application protocol is based on an assumption that the transport's
> SHOULD is really a MUST, then you end up with an application that works
> with some transport implementations, but not other -- conforming! --
> implementations.


I agree, but we aren't specifying the entire API, and I'm not sure that we
want to resolve all potential API inconsistencies here.

> We could include language in this section about priorities being important
> > to avoid deadlocks when an application has dependencies across streams.
>
> What would this advice be?  "Consume *all data* from higher priority
> streams before consuming data from lower priority streams?"


Yes, to avoid deadlock.


>
>   - Dmitri.
>