igb(4) Raising IGB_MAX_TXD ??

[Sean Bruno]

On Wed, 2012-04-18 at 09:49 -0700, Sean Bruno wrote:
> ok, good.  that at least confirms that I correctly translated between
> the driver code and documented specification.  
> 
> I will try 8k as a test for now and see how that runs.  
> 
> sean

For now, I've patched one front end server with: 
/usr/src/sys/dev/e1000/if_igb.h:#define IGB_MAX_RXD             4096 * 4

And adjusted hw.igb.rxd: 8192

So far so good, been running in production for a couple of hours so the
"smoke test" for this setting seems to be happy.

We'll continue to adjust and test tomorrow during higher load
conditions.

Sean