linux-kernel - Re: How to accelerate tcp retransmition

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Message-ID: <4F1EF104.1040107@hp.com>
Date:	Tue, 24 Jan 2012 09:57:24 -0800
From:	Rick Jones <rick.jones2@...com>
To:	leno soff <lnxuff@...il.com>
CC:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	eric.dumazet@...il.com, davem@...emloft.net
Subject: Re: How to accelerate tcp retransmition

On 01/24/2012 06:09 AM, leno soff wrote:
> On Tue, Jan 24, 2012 at 4:58 PM, leno soff<lnxuff@...il.com>  wrote:
>> Hello everyone,
>>    I have a lot of client, say C1, C2, .. Cn, which route packets to
>> my servers through router R. But R will drop 70% - 90% _ non-SYN _
>> packets from clients to Server.

I think you should address that first - why does the router drop 70 to 
905 of the non-SYN segments it receives.  At first blush that sounds 
like a classic case of massive over-subscription, and any attempt to 
accelerate the retransmissions seems destined to trigger congestive 
collapse.

As a side issue, if the router is dropping 70 to 90% of the non-SYN 
segments, why is it not also dropping 70 to 90% of the SYN segments?

Also, I'm reasonably confident that an actual keepalive probe would not 
(or at least should not?) be considered in the three duplicate ACK 
heuristic.

rick jones
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