[Beowulf] Question on clock skew of LANai

송효정 hjsong at samsung.com
Thu Jul 22 01:51:53 PDT 2004


I am Hyo Jung Song from Samsung Electronics. 
For our research & development, 
we are very interested in Myrinet switches. 

At this time, 
we need some information on Myrinet-2000. 

Specifically, we want to know following information. 
If you give me some details, 
it would be helpful to proceed our R&D. 

For Small Myrinet-2000 Switches, I would like to know the *actual value* of the below parameter :

- routing delay 
the time for the Myrinet-2000 Switch to process the header flit of a packet 
(i.e. to decide the output link depending on the routing info. in the header flit) plus the time for the switch (crossbar) to transfer the header flit from the input link to the assigned output link 

- switching delay
; the time for the switch to transfer a non-header(data) flit from the input link to the assigned output link

- flow control delay
; Assuming that stop and go flow control is used for the link level flow control. 

a. the time for the sender switch to generate the stop flit upon some predefined condition (i.e. buffer occupancy) (the time excludes the actual tranfer time to transfer the stop flit over the link, 
and counts delay only inside the switch)

b. the time for the receiver switch to decide not to send any more data upon the stop flow control.

I suppose there is a flow controller inside a switch to implement stop and go control. 
Basically, what i want to know is *the time to operate flow controller inside a switch* upon "stop" part. And I assume the time is almost same as go part. 

Besides, as for the NIC, can we get the clock skew #s in the ppm unit?

Thank you very much. 

Hyo Jung Song
Senior Engineer
Samsung Electronics 
tel. 82-2-3416-0355

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