On Wed, Jan 25, 2006 at 03:11:16PM -0800, Jason Thorpe wrote:
> 
> On Jan 25, 2006, at 11:50 AM, Pavel Cahyna wrote:
> >Do you have any explanation why does it help?
> 
> No need to copy data coming in from the chip?

are we talking about the cost of copying 4 bytes of data per frame? or
rather some more costly mbuf rearranging in the vlan(4) driver?

> >Could be HW tagging made conditional on some setting, like hardware
> >checksums (if the hardware allows turning them off)?
> 
> Why would you want to turn them off if the hardware supports it?  How many 
> VLANs are you working with, anyway?  Looking them up is almost certainly 
> cheaper than copying data that is guaranteed not to be in cache.

I want to turn them off to avoid bugs such as the one which started this
thread, and to get useful output from tcpdump.

BTW why do people want to turn hw checksumming off?

Pavel