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SubjectRe: Raise initial congestion window size / speedup slow start?
On 14/07/2010 19:15, David Miller wrote:
> From: Bill Davidsen<davidsen@tmr.com>
> Date: Wed, 14 Jul 2010 11:21:15 -0400
>
>
>> You may have to go into /proc/sys/net/core and crank up the
>> rmem_* settings, depending on your distribution.
>>
> You should never, ever, have to touch the various networking sysctl
> values to get good performance in any normal setup. If you do, it's a
> bug, report it so we can fix it.
>

Just checking the basics here because I don't think this is a bug so
much as a, less common installation that differs from the "normal" case.

- When we create a tcp connection we always start with tcp slow start
- This sets the congestion window to effectively 4 packets?
- This applies in both directions?
- Remote sender responds to my hypothetical http request with the first
4 packets of data
- We need to wait one RTT for the ack to come back and now we can send
the next 8 packets,
- Wait for the next ack and at 16 packets we are now moving at a
sensible fraction of the bandwidth delay product?

So just to be clear:
- We don't seem to have any user-space tuning knobs to influence this
right now?
- In this age of short attention spans, a couple of extra seconds
between clicking something and it responding is worth optimising (IMHO)
- I think I need to take this to netdev, but anyone else with any ideas
happy to hear them?

Thanks

Ed W


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