Re: [PATCH] skbuff: Add new tc classify variable

On Tue, 7 Feb 2012 20:57:29 +0100
Simon Wunderlich [off-list ref] wrote:

On Tue, Feb 07, 2012 at 11:05:22AM -0800, Stephen Hemminger wrote:

quoted

On Tue,  7 Feb 2012 19:39:08 +0100
Simon Wunderlich [off-list ref] wrote:

I don't understand why this is better, we already have mark to do this.
Your method saves adding a tc filter to map mark to classid, but that is hardly
a huge burden.

Unfortunately, it is. We have previously built our trees by setting marks with iptables
and matching the masks with tc and the u32 matcher, but we got a rather big performance
impact as soon as the number of users grow. The target platform are WiFi access points.
By using the proposed patch, the performance stays nearly constant at a growing number
of users.

The problem then is not the use of marks but having to add a filter rule for
each mark. We need something like u32 hash but for marks to build a table
of mark -> class id.  The current method uses a linear list of filter rules,
which is an obvious bottleneck with lots of classes.