netdev - Re: [PATCH] rfc: ethtool: early-orphan control

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Message-ID: <1292046380.3136.24.camel@localhost>
Date:	Sat, 11 Dec 2010 05:46:20 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Simon Horman <horms@...ge.net.au>
Cc:	netdev@...r.kernel.org, Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH] rfc: ethtool: early-orphan control

On Sat, 2010-12-11 at 14:39 +0900, Simon Horman wrote:
> On Sat, Dec 11, 2010 at 02:04:47PM +0900, Simon Horman wrote:
> > On Sat, Dec 11, 2010 at 04:37:58AM +0000, Ben Hutchings wrote:
> > > On Sat, 2010-12-11 at 13:13 +0900, Simon Horman wrote:
> > > > Early orphaning is an optimisation which avoids unnecessary cache misses by
> > > > orphaning an skb just before it is handed to a device for transmit thus
> > > > avoiding the case where the orphaning occurs on a different CPU.
> > > > 
> > > > In the case of bonded devices this has the unfortunate side-effect of
> > > > breaking down flow control allowing a socket to send UDP packets as fast as
> > > > the CPU will allow. This is particularly undesirable in virtualised
> > > > network environments.
> > > > 
> > > > This patch introduces ethtool control of early orphaning.
> > > > It remains on by default by it now may be disabled on a per-interface basis.
> > > > 
> > > > I have implemented this as a generic flag.
> > > > As it seems to be the first generic flag that requires
> > > > no driver awareness I also supplied a default flag handler.
> > > > I am unsure if any aspect of this approach is acceptable.
> > > 
> > > I'm not convinced that this belongs in the ethtool API.  It doesn't seem
> > > to have anything to do with hardware or driver behaviour.  The flag
> > > belongs in priv_flags, not features.
> > 
> > Ok, I have no objection to it going in priv_flags so long
> > as it can be exposed to user-space in some sensible fashion.
> > Do you have any thoughts on how best to achieve that?
> 
> Sorry, I realise that was a pretty silly question
> as I now see ETHTOOL_GPFLAGS and ETHTOOL_SPFLAGS.

Not a silly question.  The ETHTOOL_{G,S}PFLAGS commands are for
driver-specific flags while net_device::priv_flags is used by the
networking core and some special drivers (IFF_802_1Q_VLAN etc. in
<linux/if.h>).

Ben.

-- 
Ben Hutchings, Senior Software Engineer, Solarflare Communications
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

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