[PATCH] make tg3 NAPI support configurable

[Robert Olsson <Robert.Olsson@xxxxxxxxxxx>]

Greg Banks writes:

 > I've been having some issues with irq rates and cpu usage in the
 > tg3 driver.  In short, on Altix machines they're far too high.
 > It turned out that reverting the driver to its pre-NAPI interrupt
 > coalescing scheme made the situation a lot better.
 > 
 > How much better?  Running 8192 byte UDP packets across gige
 > with NAPI takes 99.5% of a CPU to service 29,100 irqs per second.
 > With the pre-NAPI code the figures are 36.0% CPU and 4880 irq/sec.
 > Similar improvements are seen for non-fragmented UDP and for TCP.

 Hello!

 You can use coalescing with NAPI as well, e1000 and other drivers
 are doing this. This will give you same interrupt rates as non-
 NAPI at low load and "polling" without any interrupts at high load.

 Furthermore NAPI can be extended to schedule dev->poll even for TX-
 interrupts. There is pacth for e1000 doing this. We see about 5-8% 
 overall system packet improvement with this.

 Cheers.
                                        --ro