netdev - Re: GRO aggregation

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Date:	Thu, 13 Sep 2012 09:36:49 +0300
From:	Shlomo Pongartz <shlomop@...lanox.com>
To:	Rick Jones <rick.jones2@...com>
CC:	Eric Dumazet <eric.dumazet@...il.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: GRO aggregation

On 9/12/2012 7:52 PM, Rick Jones wrote:
> On 09/12/2012 09:34 AM, Shlomo Pongartz wrote:
>> On 9/12/2012 7:23 PM, Rick Jones wrote:
>>> On 09/12/2012 07:41 AM, Shlomo Pongartz wrote:
>>>> Hi Eric
>>>>
>>>> The TSO is just a mean to create a burst of frames on the wire so the
>>>> NAPI will be able to pool as much as possible.
>>>
>>> Is it?  If I recall correctly, TSO was in place well before all
>>> drivers were using NAPI.  And NAPI was being proposed independent of
>>> TSO. TSO is there to save CPU cycles on the transmit side. "On the
>>> wire" what it sends is to be identical to what a host with greater CPU
>>> performance could accomplish.
>>>
>>> rick jones
>>>
>> Hi Rick.
>>
>> What I say is that I use TSO on the machine that transmits so I'll have
>> a burst of frames on the wire for the NAPI on the receiver machine.
>
> Also, NAPI was in place before GRO.  IIRC, the napi code was simply a 
> convenient/correct/natural place to have the GRO functionality.
>
> rick jones
>
Hi Rick

The thing is that napi_complete calls napi_gro_flush so this pose a 
limit on the aggregation.
However when I count the number of packets received until this routine 
is been called, I get a number,
which is bigger then what I see with tcpdump, and this number is less 
than what is expected if the limit is 64K.
So I what to know what can I do in order to improve things, e.g. 
allocate the skb differently.

Shlomo


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