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Re: [Xen-devel] [0/5] [NET]: Add TSO support

On 29 Jun 2006, at 01:20, Herbert Xu wrote:

Another question: why are gso_size and gso_segs both required? Surely
those, plus the overall request size, are redundant. e.g., shouldn't
gso_segs = tot_size / gso_size (rounded up)?

For TSO, gso_segs can be easily determined from the packet and gso_size.
However, for GSO, we don't know the packet header length so the same is
not true.

Each segment will need a header though, I'd imagine, so whoever does the segmentation needs to know the packet header length? Maybe I'm just confused. :-) Could you briefly explain what the inter-domain data format would be (e.g., is there a header, etc.), and gso_{size,segs}, for some arbitrary IP-encapsulated protocol? And how that information would be used to perform segmentation in the backend domain? Is the segmentation algorithm any different at all when the protocol is specifically TCPv4? I'd like to add some documentation of all this to netif.h when I have it clear in my head.

The patches you sent look fine. I'd really like to understand this stuff before turning it on though.

 -- Keir

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