Subject: Re: [PATCH] [TCP] Sysctl: document tcp_max_ssthresh (Limited Slow-Start)

From: Rick Jones <[email-masked]>
Date: Fri, 18 May 2007 12:39:17 -0700

Baruch Even wrote:
> Ilpo Järvinen wrote:
> 
>>Signed-off-by: Ilpo Järvinen <[email-masked]>
>>---
>> Documentation/networking/ip-sysctl.txt |   13 +++++++++++++
>> 1 files changed, 13 insertions(+), 0 deletions(-)
>>
>>diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
>>index ce16e6a..44ba8d4 100644
>>--- a/Documentation/networking/ip-sysctl.txt
>>+++ b/Documentation/networking/ip-sysctl.txt
>>@@ -239,6 +239,19 @@ tcp_max_orphans - INTEGER
>> 	more aggressively. Let me to remind again: each orphan eats
>> 	up to ~64K of unswappable memory.
>> 
>>+tcp_max_ssthresh - INTEGER
>>+	Limited Slow-Start for TCP with Large Congestion Windows defined in
>>+	RFC3742. Limited slow-start is a mechanism to limit grow of the
> 
> 
> s/grow/growth/
> 
> 
>>+	congestion window on the region where congestion window is larger than
>>+	tcp_max_ssthresh. A TCP connection with a large congestion window could
>>+	have its congestion window increased by thousand (or even more)
>>+	segments per RTT by the traditional slow-start procedure which might be
>>+	counter-productive to TCP performance when packet losses start to
>>+	occur. With limited slow-start TCP increments congestion window at
>>+	most tcp_max_ssthresh/2 segments per RTT when the congestion window is
> 
> 
> I'm not a native English speaker but "at most" sounds a bit awkward to
> me, maybe change it to "by no more than". But I'm sure someone can find
> a better phrasing.

It could be "by at most" or "by no more than" but indeed it should not just be 
"at most."

Also, it should be "With limited slow-start TCP increments the congestion 
window..."   Combining with other nits yeilds:

Limited Slow-Start for TCP with Large Congestion Windows is defined in RFC3742. 
  Limited slow-start is a mechanism to limit growth of the congestion window 
when the congestion window is larger than tcp_max_ssthresh.  A TCP connection 
with a large congestion window could have its congestion window increased by 
thousands of segments (or more) per RTT via the traditional slow-start 
procedures. This might degrade TCP performance when packet losses start to 
occur.  With limited slow-start, TCP increments the congestion window by at most 
tcp_max_ssthresh/2 segments per RTT when the congestion window is is above 
tcp_max_ssthresh.

rick jones

as an asside, "tcp_max_ssthresh" sounds like the maximum value ssthresh can 
take-on.  is that correct, or is this more of a "once ssthresh is above this, 
behave in this new way?"  If that is the case, while the horse has probably left 
the barn, perhaps another name would be better?

> 
> Baruch
> -
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