What is rx_processing_limit sysctl for Intel igb NIC driver?

[John Baldwin]

On Sunday, September 02, 2012 10:41:15 pm Andy Young wrote:
> I am tuning our server that has an Intel 82576 gigabit NIC using the igb
> driver. I see a lot of posts on the net where people bump the
> rx_processing_limit sysctl from the default value of 100 to 4096. Can
> anyone tell me what this is intended to do?

If you have multiple devices sharing an IRQ with igb (and thus are not using 
MSI or MSI-X), it forces the driver to more-or-less cooperatively schedule 
with the other interrupts on the same IRQ.  However, since igb uses a fast 
interrupt handler and a task on a dedicated taskqueue in the non-MSI case now, 
I think it doesn't even do that.  It should probably be set to -1 (meaning
unlimited) in just about all cases now.

-- 
John Baldwin