[Cialug] NIC teaming

[Zachary Kotlarek]

On May 14, 2008, at 3:50 PM, Paul Gray wrote:

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> Nathan C. Smith wrote:
>> Anyone teaming nics/bonding nics under Linux?  Did you realize any  
>> measurable advantage by doing it?  Any Gotchas?
>
> The gotchas relate to saturating the PCI bus with interrupts.  If  
> you're
> bonding a couple of GigE nics together, there's a benefit, but more  
> than
> two and your PCI/PCI-X bus cannot keep up with the interrupts.
>
> Just my experience.

GigE without interrupt mitigation is a bad time. But many popular  
drivers support on-card interrupt coalescence. For example, the E1000  
driver accepts the parameter InterruptThrottleRate=X -- if set to a  
number greater than 100 the card will limit interrupts to X per  
second. Setting it to say, 2000 or 3000 will keep you from getting  
into interrupt-deathtrash without much risk of losing packets under  
normal loads.

If you've got a high-load system, be sure you've got NAPI enabled.  
It's overkill for systems that rarely reach gig+ speeds, and it does  
add a small amount of latency, but if you're got a busy card(s) it can  
all but eliminate packet-related interrupts by disabling them  
altogether and polling at regular intervals instead. Many of the  
popular 1000 Mbit drivers support it now -- including Forcedeth, Via- 
Rhine, and E1000 -- but IIRC it is not enabled by default, so be sure  
to check your kernel config.

	Zach
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