xl(4) & polling

Subhro subhro.kar at gmail.com
Wed May 11 08:11:34 PDT 2005

On 5/11/2005 13:57, Tuomo Latto wrote:

> 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.
Silly me :(. I meant something, typed something else. Its indeed the 
other way round. Thanks to everyone who pointed this out.


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