netdev - Re: [RFC] GRO scalability

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Date:	Mon, 08 Oct 2012 19:55:55 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rick Jones <rick.jones2@...com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, Jesse Gross <jesse@...ira.com>
Subject: Re: [RFC] GRO scalability

On Mon, 2012-10-08 at 10:49 -0700, Rick Jones wrote:

> So, with my term shuffle better defined, let's circle back to your 
> proposal to try to GRO-service a very much larger group of flows, with a 
> "flush queued packets older than N packets" heuristic as part of the 
> latency minimization.  If N were 2 there - half the number of flows, the 
> "perfect" shuffle" doesn't get aggregated at all right? N would have to 
> be 4 or the number of concurrent flows.   What I'm trying to get at is 
> just to how many concurrent flows you are trying to get GRO to scale, 
> and whether at that level you have asymptotically approached having a 
> hash/retained state that is, basically, a duplicate of what is happening 
> in TCP.
> 

I didnt said "flush queued packets older than N packets" but instead
suggested to use a time limit, eventually a sysctl.

"flush packet if the oldest part of it is aged by xxx us"

Say the default would be 500 us

If your hardware is capable of receiving 2 packets per us, this would
allow 1000 packets in GRO queue. So using a hash table with 128 slots,
and keeping the current limit of 8 entries per bucket would allow this
kind of workload.

If your hardware is capable of receiving one packet per us, this would
allow 50 packets in GRO queue.



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