netdev - Re: [RFC] NAPI as kobject proposal

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Message-ID: <4B69ECE5.7060803@caviumnetworks.com>
Date:	Wed, 03 Feb 2010 13:38:45 -0800
From:	David Daney <ddaney@...iumnetworks.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	Stephen Hemminger <shemminger@...tta.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [RFC] NAPI as kobject proposal

Ben Hutchings wrote:
> On Fri, 2010-01-29 at 10:18 -0800, Stephen Hemminger wrote:
>> The NAPI interface structure in current kernels is managed by the driver.
>> As part of receive packet steering there is a requirement to add an
>> additional parameter to this for the CPU map. And this map needs to
>> have an API to set it.
>>
>> The right way to do this in the kernel model is to make NAPI into
>> a kobject and associate it back with the network device (parent).
>> This isn't wildly difficult but does change some of the API for
>> network device drivers because:
>>   1. They need to handle another possible error on setup
>>   2. NAPI object needs to be dynamically allocated
>>      separately (not as part of netdev_priv)
>>   3. Driver should pass index that can be uses as part of
>>      name (easier than scanning)
>>
>> Eventually, there will be:
>>   /sys/class/net/eth0/napi0/
>>                             weight
>>                             cpumap
> 
> I think the NAPI objects should be created as children of a bus device
> and then linked from the net device directories, e.g.
> 
> /sys/devices/.../ net/eth0/
>                            napi0 -> ../../napi/napi0
>                       eth1/
>                            napi0 -> ../../napi/napi0
>                   napi/napi0/
>                              weight
>                              cpumap
> 

This seems right.

Some drivers have a single napi object logically associated with 
multiple interfaces.  Although the current architecture forces us to 
associate the napi object with a single net_device, it would be nice to 
move towards something that allows sharing a napi object between 
multiple devices.

David Daney
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