Subject: Re: [Ipoverib] comments on draft-kashyap-ipoib-connected-mode-02.txt

From: "H.K. Jerry Chu" <[email-masked]>
Date: Mon, 22 Nov 2004 18:43:04 -0800 (PST)

>>I'm not sure what you mean by the last two sentences above. MTU value must
>>be made known to the IP layer so that latter won't send anything larger
>>than that. Otherwise the pkt will get dropped by the IB layer (unless the
>>latter performs SAR, which is a bad idea).
>
>One might argue that *C is focused on an equivalence to TSO (large send) 
>thus the logical MTU is not required.

Interesting idea. But I thought for the *C modes it's an error if one
end post a send that is larger in size than the WQE posted to the receive
queue. If this is true then unless the receiver always posts 2**32 buffer,
you'll still need the MTU concept to put a reasonable cap on the buffer
size the receive side must prepare.

>One might argue that the logical MTU 
>represents an asymmetric maximum receive buffer that will be posted thus 
>messages must be sent that do not exceed this maximum.  One might argue 
>that having a single buffer size independent of the *C / UD being used 
>maximizes KISS.

This limits the MTU down to the UD MTU, which defeats one of the main
benefits of using *C modes.

>I'm open to exploring these options but do not believe all 
>must be supported.

So it looks to me only the middle one makes sense.

Jerry

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