Polling For 100 mbps Connections? (Was Re: Freebsd Theme Song)

Drew Tomlinson drew at mykitchentable.net
Mon Dec 12 12:30:41 PST 2005

On 12/12/2005 8:13 AM Ted Mittelstaedt wrote:

>  Fundamentally, here's the problem Danial is claiming exists:
>it takes a certain amount of time to get the packet clocked in
>from the network into the ethernet receiver.  This is hardware
>dependent and cannot be changed.
>It takes a certain amount of time to get the packet out of
>the hardware in the ethernet card into main ram, this also
>hardware dependent and cannot be changed. (unless the device
>driver is terribly inefficient, which we will assume it's not)
>Once in main ram, the information in the packet has to go through
>a number of code statements.  The more code statements the
>longer the information in the packet is sitting around in
>the FreeBSD system's memory.
>It then takes a certain amount of time to get the information
>out of main memory into the other sending ethernet nic's buffers,
>and it takes time to get it out of the sending nic back to the
>Danial is claiming the slowness is in the main ram section of
>things, not in the ethernet driver code.
>polling makes the ethernet driver more efficient at high data
>rates, but it does nothing for the speed of processing within
>the TCPIP stack itself.  At low data rates polling is less
>efficient than the interrupt method.  And unless the nic driver
>is terribly inefficient to start with, the time it adds to the
>packet path in the system is minor compared to the time spent
>in the TCP/IP stack.

Thanks for the explanation.  So would polling be beneficial or 
detrimental for a 100 mbps Ethernet card?  Not sure if 100 mbps is 
considered "high" or "low" speed.  I'm specifically interested in 
NetGear cards using the dc driver or DLink cards using the rl driver.



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