netdev - Re: [ethtool PATCH 2/2] Add RX packet classification interface

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Date:	Mon, 07 Mar 2011 18:28:01 +0000
From:	Ben Hutchings <bhutchings@...arflare.com>
To:	Dimitris Michailidis <dm@...lsio.com>
Cc:	Alexander Duyck <alexander.h.duyck@...el.com>,
	Santwona Behera <santwona.behera@....com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [ethtool PATCH 2/2] Add RX packet classification interface

On Mon, 2011-03-07 at 10:22 -0800, Dimitris Michailidis wrote:
> Ben Hutchings wrote:
> > On Mon, 2011-03-07 at 09:04 -0800, Alexander Duyck wrote:
> >> The only time where location really matters is if you are attempting to 
> >> overwrite an existing rule and I am not sure how that would be handled 
> >> in ntuple anyway since right now adding additional rules via ntuple for 
> >> ixgbe just results in duplicate rules being defined.
> > 
> > As I understand it, the location also determines the *priority* for the
> > rule.
> 
> This is true, at least for TCAMs.  But it's relevant only when multiple 
> filters would match a packet.  People often use non-overlapping filters, for 
> these adding the filter at any available slot is OK.

Right.  But ethtool would have to determine that the filter was non-
overlapping, before ignoring the location.  Also it cannot allow
deletion by location if it ever ignores the location on insertion.  We
should make the location optional at both the command-line and API
level, but never ignore it.

> > Which is why I wrote that "@fs.@...ation specifies the index to
> > use and must not be ignored."
> > 
> > To support hardware where the filter table is hash-based rather than a
> > TCAM, we would need some kind of flag or special value of location that
> > means 'wherever'.
> 
> I'd find the 'wherever' option useful for TCAMs too.  Maybe even have a few 
> of those, like 'first available', 'any', and 'last available'.  The last one 
> is quite useful for catch-all rules without requiring one to know the TCAM size.

Agreed.

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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