Re: What are the issues related to increasing Rx ring size ?

[ Sorry for the late reply. I just came back from holiday... ]

On Thu, 23 Sep 2004, Amitava Biswas wrote:

> I want to use this driver under a situation when packets arrive in
> bursts (few hundered to say one thousand small (64Byte) packets in
> one burst).

Maybe NAPI could also help. I think that I've seen NAPI patches for 
3c59x posted on netdev.

> Perhaps this simple information is available in the NIC specs, which
> is not a public domain doc. I am expecting that some driver writer
> has this, and can kindly share this information or the document
> itself or a tip on how to get it from 3 com (I would be grateful).

Sorry, but this is not possbile due to the rules that we agreed to 
when we downloaded the document from 3Com. There was somebody from 
3Com that wrote some months ago promising to look after making the 
docs available again, but I last time I checked (~2 months ago) they 
were still not to be found on 3Com's site.

> 2) What are the other issues which may be the hurdles or constraints
> to the driver operation with large Rx ring size ? These may be both
> - system / resource constraints and performance constraints.

I would like to add to Donald's answer another issue:  
max_interrupt_work is a parameter that limits (among others) the
amount of packets that can be processed in one call to the interrupt
routine. The default values for max_interrupt_work and for the Rx ring
size are pretty close (or identical, depending on the driver version)  
which allows a complete processing of a full Rx ring in one call of
the interrupt routine. If latency is important, you should probably
increase max_interrupt_work to be close to the Rx ring size - but be
prepared for the system to spend lots of time dealing with network
packets and not be responsive for anything else; otherwise, although
the packets will be queued and not lost, they will not reach the upper
layers until later on after the interrupt routine was called lots of
times.

-- 
Bogdan Costescu

IWR - Interdisziplinaeres Zentrum fuer Wissenschaftliches Rechnen
Universitaet Heidelberg, INF 368, D-69120 Heidelberg, GERMANY
Telephone: +49 6221 54 8869, Telefax: +49 6221 54 8868
E-mail: [email protected]

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