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Add a section on flow control performance #3793

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Jul 14, 2020
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Add a section on flow control performance #3793

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Add a section on flow control performance
martinthomson Jun 26, 2020
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Remove problematic paragraph
martinthomson Jul 7, 2020
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martinthomson Jul 9, 2020
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Add note about gaps in receive buffers
martinthomson Jul 14, 2020
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martinthomson Jul 14, 2020
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martinthomson Jul 14, 2020
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11 changes: 11 additions & 0 deletions draft-ietf-quic-transport.md
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Expand Up @@ -968,6 +968,17 @@ signal before advertising additional credit, since doing so will mean that the
peer will be blocked for at least an entire round trip, and potentially for
longer if the peer chooses to not send STREAMS_BLOCKED frames.

## Flow Control Performance

An endpoint that is unable to ensure that a peer has flow control credit in the
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order of the current BDP will have receive throughput limited by flow control
and not other limiting factors like congestion control. Timely sending of
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updates to flow control limits can improve performance, however an excessive
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rate of updates can also adversely affect performance.
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I'm not if I agree with this statement. You'd really have to take it to the extreme to affect performance. MAX_STREAM_DATA frames are small, and even if you bundle one of them with every ACK you send, this would likely not be a significant overhead.

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I tend to agree, the present working sounds like a "significant" warning, but the penalty of updating too infrequently is also severe - perhaps and example of frequently might help? such as 1/8 RTT?

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I tend to agree, the present working sounds like a "significant" warning, but the penalty of updating too infrequently is also severe - perhaps and example of frequently might help? such as 1/8 RTT?

Can the example of frequently lead to SWS?

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I'd also like to understand why you're saying it's going to adversely affect performance. MsQuic bundles FC updates with ACKs and as far as I have seen, we've been able to reach some of the highest perf numbers in testing out there.

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I suspect "excessive" means "more frequently than ACKs and/or in their own packets." Should we say that?


This document does not specify techniques for tuning flow control performance
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I don't think this paragraph is necessary, but that's me.

where resources allocated to receiving data are limited.


# Connections {#connections}

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