Re: [quicwg/base-drafts] ACK generation recommendation (#3304)
Ryan Hamilton <notifications@github.com> Tue, 17 December 2019 15:28 UTC
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From: Ryan Hamilton <notifications@github.com>
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Subject: Re: [quicwg/base-drafts] ACK generation recommendation (#3304)
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On Tue, Dec 17, 2019 at 6:48 AM Nick Banks <notifications@github.com> wrote: > Gorry raised the point that in experiments, this generates way too many > ACK packets in high bandwidth networks, such as satellite networks. This > has noticeable CPU costs for QUIC, for both sending as well as for > receiving. > > Could you expand on this? I find this to be an extremely general > statement, and not very helpful in understanding the real motivation for > any possible changes. You say it "has noticeable CPU costs for QUIC", but > are you referring to the client, server or some middle boxes somehow? > It can happen to either endpoint. Consider an HTTP/3 download. The client ends up burning a bunch of CPU *sending* ACK, and the server a bunch of CPU *processing* ACKs. > Assuming you're worried about the CPU costs on the server side, has anyone > explicitly measured the differences in CPU cost for generating different > number of ACKs per RTT? What's the effect on FC? Fewer ACKs will mean the > sender (I'm assuming the server?) is going to have to buffer more, and FC > windows might be hit more often. Is this really such a big problem that is > requires a spec change? In V1? > We've definitely noticed the CPU costs at Google on high bandwidth connections with long flow. This led us to implement a variety of ACK reduction strategies which reduced CPU use significantly. I think a QUIC sender which sends ACKs of every 2 packets without and further limits will be unable to take full advantage of the network and yes, we should explicitly permit this in V1. I don't believe we measured the impact on flow control. Our clients typically advertise a very large flow control window which basically does not get hit. Cheers, Ryan -- You are receiving this because you are subscribed to this thread. Reply to this email directly or view it on GitHub: https://github.com/quicwg/base-drafts/issues/3304#issuecomment-566590677
- Re: [quicwg/base-drafts] ACK generation recommend… mirjak
- [quicwg/base-drafts] ACK generation recommendatio… Jana Iyengar
- Re: [quicwg/base-drafts] ACK generation recommend… Lars Eggert
- Re: [quicwg/base-drafts] ACK generation recommend… Nick Banks
- Re: [quicwg/base-drafts] ACK generation recommend… Ryan Hamilton
- Re: [quicwg/base-drafts] ACK generation recommend… Ryan Hamilton
- Re: [quicwg/base-drafts] ACK generation recommend… ianswett
- Re: [quicwg/base-drafts] ACK generation recommend… mjoras
- Re: [quicwg/base-drafts] ACK generation recommend… Jana Iyengar
- Re: [quicwg/base-drafts] ACK generation recommend… Kazuho Oku
- Re: [quicwg/base-drafts] ACK generation recommend… mjoras
- Re: [quicwg/base-drafts] ACK generation recommend… Jana Iyengar
- Re: [quicwg/base-drafts] ACK generation recommend… Jana Iyengar
- Re: [quicwg/base-drafts] ACK generation recommend… Jana Iyengar
- Re: [quicwg/base-drafts] ACK generation recommend… Yang Chi
- Re: [quicwg/base-drafts] ACK generation recommend… Junho Choi
- Re: [quicwg/base-drafts] ACK generation recommend… Jana Iyengar
- Re: [quicwg/base-drafts] ACK generation recommend… ianswett
- Re: [quicwg/base-drafts] ACK generation recommend… ianswett
- Re: [quicwg/base-drafts] ACK generation recommend… Lars Eggert
- Re: [quicwg/base-drafts] ACK generation recommend… ianswett
- Re: [quicwg/base-drafts] ACK generation recommend… Lars Eggert
- Re: [quicwg/base-drafts] ACK generation recommend… Gorry Fairhurst
- Re: [quicwg/base-drafts] ACK generation recommend… Christian Huitema
- Re: [quicwg/base-drafts] ACK generation recommend… Christian Huitema
- Re: [quicwg/base-drafts] ACK generation recommend… Gorry Fairhurst
- Re: [quicwg/base-drafts] ACK generation recommend… Christian Huitema
- Re: [quicwg/base-drafts] ACK generation recommend… Gorry Fairhurst
- Re: [quicwg/base-drafts] ACK generation recommend… Dmitri Tikhonov
- Re: [quicwg/base-drafts] ACK generation recommend… Yang Chi
- Re: [quicwg/base-drafts] ACK generation recommend… mjoras
- Re: [quicwg/base-drafts] ACK generation recommend… mjoras
- Re: [quicwg/base-drafts] ACK generation recommend… ianswett
- Re: [quicwg/base-drafts] ACK generation recommend… Gorry Fairhurst
- Re: [quicwg/base-drafts] ACK generation recommend… Lars Eggert
- Re: [quicwg/base-drafts] ACK generation recommend… Martin Thomson