Re: Cost of parsing ACK frames in QUIC

[Mikkel Fahnøe Jørgensen <[e-mail]>]

While this may be true, please note that QUIC also requires that the entire
packet is valid before it does anything that modifies the state of the
receiver.

This means that you generally have to do two passes of the packet to ensure
that the packet is valid. In the first pass you can then store data for the
optimistic case of a single ACK frame.

That said, arguments about fast(er) processing still apply, but it is no
longer limited to only ACK frames.


On 10 May 2018 at 16.25.50, Deval, Manasi ([e-mail]) wrote:

Hi All,



The QUIC header definitions tend to use as few bits as possible by
implementing the policy to use variable size fields. The result of this
policy would be that each receiver needs to do a two part lookup to
identify the field and this needs to be implemented serially in order to
parse the whole frame time.



For example, in a case where no packets were dropped, a sender may receive
an ACK for a single block. If a code path were trying to determine the size
of an ACK, they would have to read 8 fields to determine the size of ACK.



A client only sees a few ACKs. Majority of the ACKs are seen on the server
side. It would be good to simplify this scheme so ACK processing can be
accelerated with SIMD instructions would be good.



Thanks,

Manasi