Re: e1000e and NAPI

[LDB]

Jolynn Schmidt wrote:
> Hi, we have some applications that receive very high packet rates, and
> have not noticed the behavior I would expect from NAPI (as I
> understand it). Does the e1000e driver support napi? If so, wouldn't I
> see the number of interrupts (as measured with sar) go down with a
> high packet rate (say, >100k). Right now, with interrupt moderation
> off for the card I'm seeing virtually 1:1 wrt packets and interrupts.
> 
> Thanks
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> 

According to Intel's documentation it is supported, but here are the
details for your perusal:

	http://downloadmirror.intel.com/15817/eng/README.txt

How did you load the module?

The documentation is very specific above, and it reads as follows:



Setting InterruptThrottleRate to 0 turns off any interrupt moderation
and may improve small packet latency, but is generally not suitable
for bulk throughput traffic.

NOTE:  InterruptThrottleRate takes precedence over the TxAbsIntDelay and
       RxAbsIntDelay parameters.  In other words, minimizing the receive
       and/or transmit absolute delays does not force the controller to
       generate more interrupts than what the Interrupt Throttle Rate
       allows.

NOTE:  When e1000e is loaded with default settings and multiple adapters
       are in use simultaneously, the CPU utilization may increase non-
       linearly.  In order to limit the CPU utilization without impacting
       the overall throughput, we recommend that you load the driver as
       follows:

           modprobe e1000e InterruptThrottleRate=3000,3000,3000

       This sets the InterruptThrottleRate to 3000 interrupts/sec for
       the first, second, and third instances of the driver.  The range
       of 2000 to 3000 interrupts per second works on a majority of
       systems and is a good starting point, but the optimal value will
       be platform-specific.  If CPU utilization is not a concern, use
       RX_POLLING (NAPI) and default driver settings.


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