netdev - Re: [RFC] net: napi fix

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Message-ID: <20071213102233.3727e9a0@freepuppy.rosehill>
Date:	Thu, 13 Dec 2007 10:22:33 -0800
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	David Miller <davem@...emloft.net>
Cc:	gallatin@...i.com, joonwpark81@...il.com, auke-jan.h.kok@...el.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	jgarzik@...ox.com, jesse.brandeburg@...el.com
Subject: Re: [RFC] net: napi fix

On Thu, 13 Dec 2007 06:19:38 -0800 (PST)
David Miller <davem@...emloft.net> wrote:

> From: Andrew Gallatin <gallatin@...i.com>
> Date: Thu, 13 Dec 2007 09:13:54 -0500
> 
> > If the netif_running() check is indeed required to make a device break
> > out of napi polling and respond to an ifconfig down, then I think the
> > netif_running() check should be moved up into net_rx_action() to avoid
> > potential for driver complexity and bugs like the ones you found.
> 
> That, or something like it, definitely sounds reasonable and much
> better than putting the check into every driver :-)
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It is not possible to do netif_running() check in generic code as currently
written because of the case of devices where a single NAPI object is
being used to handle two devices. The association between napi and netdevice
is M to N.  There are cases like niu that have multiple NAPI's and one
netdevice; and devices like sky2 that can have one NAPI and 2 netdevice's.

The existing pointer from napi to netdevice is only used by netconsole
now. For devices like sky2 it means that netconsole can't work on the the
second port which is a not a big problem. But adding a netif_running()
check would be a big issue.

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