netdev - Re: SACK scoreboard

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Message-ID: <47844D1C.1060706@psc.edu>
Date:	Tue, 08 Jan 2008 23:27:08 -0500
From:	John Heffner <jheffner@....edu>
To:	Andi Kleen <andi@...stfloor.org>
CC:	David Miller <davem@...emloft.net>, ilpo.jarvinen@...sinki.fi,
	lachlan.andrew@...il.com, netdev@...r.kernel.org,
	quetchen@...tech.edu
Subject: Re: SACK scoreboard

Andi Kleen wrote:
> David Miller <davem@...emloft.net> writes:
>> The big problem is that recovery from even a single packet loss in a
>> window makes us run kfree_skb() for a all the packets in a full
>> window's worth of data when recovery completes.
> 
> Why exactly is it a problem to free them all at once? Are you worried
> about kernel preemption latencies?
> 
> -Andi


I also wonder how much of a problem this is (for now, with window sizes 
of order 10000 packets.  My understanding is that the biggest problems 
arise from O(N^2) time for recovery because every ack was expensive. 
Have current tests shown the final ack to be a major source of problems?

   -John
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