Subject: Re: multiple Tx queues
To: Greg Troxel <>
From: Sam Leffler <>
List: tech-net
Date: 01/11/2004 11:07:30
On Sunday 11 January 2004 10:17 am, Greg Troxel wrote:
>   The Atheros 5212-based cards support multiple xmit queues and
>   implement a variety of queueing policies in h/w.  This stuff is
>   explicitly intended to supoprt QoS as set out, for example, the WME
>   spec.  Applications include VoIP and streaming video.  To
>   effectively use this stuff applications need to be able to tag
>   packets and have the OS stay out of the way except to not smash the
>   tag before it reaches the driver (where it can be used to select the
>   appropriate queue).
> I haven't read the WME/802.11e specs yet.
> Why couldn't this be handled by an application setting the TOS (er,
> DSCP) with a setsockopt, and having the driver sort into queues based
> on the DSCP?  If there is a qos mechanism for sending packets over
> wireless, then I would think it useful for it to work on packets
> originated on a wired host that are being forwarded by another host
> over wireless (e.g. connection sharing over Ethernet, etc. of a host
> with an 802.11 connection).

I thought I was saying basically this.  Some ideas were floated for 
configuring the mapping between traffic and priority and/or possible queueing 
algorithms.  I was just trying to point out that for some hardware this is 
probably not useful.  Having the OS doing anything is probably not very 
helpful; just pass the packet down to the driver as quickly as possible so it 
can stick it in the appropriate h/w queue.