Re: RFC: Nagle latency tuning

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To: Andi Kleen <andi@...>
Cc: David Miller <davem@...>, <rick.jones2@...>, <netdev@...>
Date: Monday, September 22, 2008 - 6:22 pm

Andi Kleen wrote:

It's proven a little harder than anticipated to create a trivial test case, but 
I should be able to post some traces from a freely-available app soon.


Thanks, will try.


Indeed.  Setting tcp_delack_min to 0 completely eliminated the undesired 
latencies, though of course that would be a bit dangerous with naive apps 
talking across the network.  Changing tcp_ato_min didn't do anything interesting 
for this case.


The problem is that we're trying to use one set of values for links with 
extremely different performance characteristics.  We need to initialize TCP 
sockets with min/default/max values that are safe and perform well.

How horrendous of a layering violation would it be to attach TCP performance 
parameters (either user-supplied or based on interface stats) to route table 
entries, like route metrics but intended to guide TCP autotuning?  It seems like 
it shouldn't be that hard to teach TCP that it doesn't need to optimize my lo 
connections much, and that it should be optimizing my eth0 subnet connections 
for lower latency and higher bandwidth than the connections that go through my 
gateway into the great beyond.


As long as we have hardcoded minimum delays > 10ms, I don't think there's much 
of a point, but it's something to keep in mind for the future.

-- Chris
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Messages in current thread:
RFC: Nagle latency tuning, Christopher Snook, (Mon Sep 8, 5:56 pm)
Re: RFC: Nagle latency tuning, Andi Kleen, (Mon Sep 8, 6:55 pm)
Re: RFC: Nagle latency tuning, Chris Snook, (Tue Sep 9, 1:22 am)
Re: RFC: Nagle latency tuning, Rick Jones, (Mon Sep 8, 6:39 pm)
Re: RFC: Nagle latency tuning, Chris Snook, (Tue Sep 9, 1:10 am)
Re: RFC: Nagle latency tuning, Rick Jones, (Tue Sep 9, 12:33 pm)
Re: RFC: Nagle latency tuning, Chuck Lever, (Tue Sep 9, 12:54 pm)
Re: RFC: Nagle latency tuning, Rick Jones, (Tue Sep 9, 1:54 pm)
Re: RFC: Nagle latency tuning, Arnaldo Carvalho de Melo, (Tue Sep 9, 1:21 pm)
Re: RFC: Nagle latency tuning, Andi Kleen, (Tue Sep 9, 10:36 am)
Re: RFC: Nagle latency tuning, Chris Snook, (Tue Sep 9, 2:40 pm)
Re: RFC: Nagle latency tuning, David Miller, (Tue Sep 9, 3:59 pm)
Re: RFC: Nagle latency tuning, David Miller, (Mon Sep 22, 6:49 am)
Re: RFC: Nagle latency tuning, David Miller, (Mon Sep 22, 7:09 am)
Re: RFC: Nagle latency tuning, Andi Kleen, (Mon Sep 22, 4:30 pm)
Re: RFC: Nagle latency tuning, Chris Snook, (Mon Sep 22, 6:22 pm)
Re: RFC: Nagle latency tuning, Rick Jones, (Mon Sep 22, 6:47 pm)
Re: RFC: Nagle latency tuning, Chris Snook, (Mon Sep 22, 6:57 pm)
Re: RFC: Nagle latency tuning, David Miller, (Mon Sep 22, 6:26 pm)
Re: RFC: Nagle latency tuning, Chris Snook, (Mon Sep 22, 7:00 pm)
Re: RFC: Nagle latency tuning, David Miller, (Mon Sep 22, 7:13 pm)
Re: RFC: Nagle latency tuning, Andi Kleen, (Mon Sep 22, 7:24 pm)
Re: RFC: Nagle latency tuning, David Miller, (Mon Sep 22, 7:21 pm)
Re: RFC: Nagle latency tuning, Andi Kleen, (Mon Sep 22, 8:14 pm)
Re: RFC: Nagle latency tuning, David Miller, (Mon Sep 22, 9:40 pm)
Re: RFC: Nagle latency tuning, Andi Kleen, (Mon Sep 22, 10:23 pm)
Re: RFC: Nagle latency tuning, David Miller, (Mon Sep 22, 10:28 pm)
Re: RFC: Nagle latency tuning, Andi Kleen, (Mon Sep 22, 10:41 pm)
Re: RFC: Nagle latency tuning, Rick Jones, (Mon Sep 22, 8:33 pm)
Re: RFC: Nagle latency tuning, Andi Kleen, (Mon Sep 22, 10:12 pm)
Re: RFC: Nagle latency tuning, Chris Snook, (Tue Sep 9, 4:25 pm)
Re: RFC: Nagle latency tuning, Andi Kleen, (Tue Sep 9, 3:07 pm)
Re: RFC: Nagle latency tuning, Chris Snook, (Thu Sep 11, 12:08 am)
Re: RFC: Nagle latency tuning, Arnaldo Carvalho de Melo, (Tue Sep 9, 3:21 pm)
Re: RFC: Nagle latency tuning, David Miller, (Tue Sep 9, 1:17 am)
Re: RFC: Nagle latency tuning, Chris Snook, (Tue Sep 9, 1:56 am)
Re: RFC: Nagle latency tuning, Evgeniy Polyakov, (Tue Sep 9, 2:22 am)
Re: RFC: Nagle latency tuning, Arnaldo Carvalho de Melo, (Tue Sep 9, 9:00 am)
Re: RFC: Nagle latency tuning, Chris Snook, (Tue Sep 9, 2:28 am)
Re: RFC: Nagle latency tuning, David Miller, (Tue Sep 9, 2:02 am)
Re: RFC: Nagle latency tuning, Mark Brown, (Tue Sep 9, 6:31 am)
Re: RFC: Nagle latency tuning, David Miller, (Tue Sep 9, 8:05 am)
Re: RFC: Nagle latency tuning, Mark Brown, (Tue Sep 9, 8:09 am)
Re: RFC: Nagle latency tuning, David Miller, (Tue Sep 9, 8:19 am)