netdev - Re: netif_napi_add vs. multiple netdev's

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Date:	Tue, 16 Oct 2007 09:10:35 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	benh@...nel.crashing.org
Cc:	netdev <netdev@...r.kernel.org>
Subject: Re: netif_napi_add vs. multiple netdev's

On Tue, 16 Oct 2007 15:47:13 +1000
Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:

> Hi Stehphen !
> 
> The new netif_napi_add() function takes a netdev argument. In the EMAC
> case, there is one NAPI instance working on behalf of multiple netdev's,
> so that isn't very useful. For my EMAC patch (just posted to you & the
> list), I'm not passing NULL, but I'm wondering what would be a good way
> to handle netpoll here...

The problem is that netpoll only has a handle to the device being used
as a netconsole, but may need to activate the NAPI poll routine to
cleanup state. Perhaps teaching netpoll about N to 1 mappings would
be better.

> 
> The way it's currently implemented, there's a list of NAPI's attached to
> the netdev, so obviously, that won't work for my usage scenario.

sky2 driver has potentially 2 ports for 1 NAPI instance.

> I'm not sure what's the best data structure that would be suitable for
> both N ndev's for 1 NAPI and 1 ndev for N NAPI's though... I could
> allocate "stub" list heads and queue those up, but that's a bit gross...

The new interface doesn't change anything. The old code had the
same problem vis-a-vis netpoll.

-- 
Stephen Hemminger <shemminger@...ux-foundation.org>
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