Patrick Geoffray patrick at myri.com
Mon Oct 15 08:50:11 PDT 2001

Hi Hong,

Hong Ong wrote:

>   currently, I am trying to compile a list of NICs that support
> programed I/O (PIO). However, I only manage to find one which is
> Myrinet.
>   if you know any others, could you please send me the name of the NIC
> and/or vendor website? Also, if possible, could you please give
> your comments/recommendation about the NIC, e.g. good, bad, ease of use,
> cost vs. performance, has Linux driver, etc.

Every PCI devices on the planet supports PIO. The processor can 
always read/write to PCI memory, even if it's a SCSI interface or 
a Video card.

So if you ask which NICs supports PIO, I would say all of them. 
This is the only way to communicate from the CPU to the NIC. 
Now, is it smart to use PIO for everything ? Hell no ! 
Your CPU cycles are precious, you certainely want to use them 
to do something usefull, not to copy data over the PCI bus. 
DMAs are much more efficient to do this silly job. The drawback 
is the DMA initialisation cost that increases a little bit the 
latency, but it's there is no cost for your host.

Interconnects people should always keep in mind that the CPUs 
are here to run the code, not to support the interconnects.


|   Patrick Geoffray, Ph.D.      patrick at myri.com 
|   Myricom, Inc.                http://www.myri.com
|   Cell:  865-389-8852          685 Emory Valley Rd (B)
|   Phone: 865-425-0978          Oak Ridge, TN 37830

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