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Re: [Xen-devel][PATCH] VNIF: Using smart polling instead of event notification.

On 10/02/09 02:41, Ian Campbell wrote:
> On Thu, 2009-10-01 at 15:02 +0100, Xu, Dongxiao wrote:
>> We found that the event notification frequency is still high in some network 
>> cases. NAPI polls only for a little
>> time slot and does not efficient enough in our backend/frontend case. 
>> Actually our patch repeated calling NAPI
>> interface to do more polling, and netback will NOT notify netfront during 
>> this period. Once netfront polling out
>> all the data, and finds that there is no more data arrive/send during the 
>> next 100ms, the timer will stop working 
>> to end the polling. 
> Isn't that an argument for improving NAPI rather than coding workarounds
> into each driver? As physical NICs increase in speed it seems like NAPI
> will need to increase its efficiency in a similar manner.
> It would be interesting to run the patches past netdev@vger.

Yes.  NAPI is intended to address precisely this issue, so it should be
made to work.

>>     This filed 'smart_poll_active' is shared by netfront and netback,
>> to indicate whether netfront is polling data. 
>> So this filed is necessary for netback to notify netfront if this flag
>> is not set. 
> Right, but that doesn't justify sticking a netfront specific field in a
> generic ring structure.

This kind of poll/interrupt switch isn't network-specific though; this
just happens to be the first user.   Presumably other devices with a
high rate of small messages could also take advantage of it.


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