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Date: Wed, 17 Dec 2014 14:02:03 +0100
From: Olivier MATZ <olivier.matz@6wind.com>
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To: Helmut Sim <simhelmut@gmail.com>, Alex Markuze <alex@weka.io>
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Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] two tso related questions
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Hi Helmut,

On 12/17/2014 08:17 AM, Helmut Sim wrote:
>>>>> While working on TSO based solution I faced the following two questions:
>>>>>
>>>>> 1.
>>>>> is there a maximum pkt_len to be used with TSO?, e.g. let's say if
>>>>> seg_sz
>>>>> is 1400 can the entire segmented pkt be 256K (higer than 64K) ?, then
>>>>> the
>>>>> driver gets a list of chanined mbufs while the first mbuf is set to TSO
>>>>> offload.

I think the limitations depend on:

- the window size advertised by the peer: your stack should handle this
   and not generate more packets that what the peer can receive

- the driver: on ixgbe, the maximum payload length is 2^18. I don't know
   if there is a limitation on number of chained descriptors.

I think we should define a way to know this limitation in the API. Maybe
a comment saying that the TSO length should not be higher than 256KB (or
fix it to 64KB in case future drivers do not support 256KB) is enough.

Regards,
Olivier