xl(4) & polling

Tuomo Latto djv at mbnet.fi
Wed May 11 01:27:46 PDT 2005

Subhro wrote:
> In Device Polled systems, the NIC does not generate any interrupt at 
> all. Instead whenever the packets arrive at a Network interface, they 
> are captured and put into a queue. The kernel scheduler checks the quese 
> at regular intervals and processes the packets which are waiting. This 
> interval is adjusted by the "options HZ=x" kernel option.
> If the value of x is very high, there may eb two scenarios. In the first 
> scenario, the queue may fill up and subsequent packets are dropped. In 
> this case retransmission of the packets are required. In the second 
> scenario, the packets would be held up for excessive long times which 
> defeats the entire purpose of Device Polling. If the value of x is very 
> low, the scheduler would check the queue frequently and would again 
> defeat the entire idea of Device Polling.

It's the other way around. Large values indicate larger polling frequency
thus amounting to more checks. Or at least the name of the option would
suggest that anyway.


... I can walk on water, but I stagger on alcohol

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