[Beowulf] Re: typical latencies for gigabit ethernet

Scott Atchley atchley at myri.com
Mon Jun 29 14:04:50 EDT 2009


On Jun 29, 2009, at 1:44 PM, Scott Atchley wrote:

>> Right, and that's what I did before, with sensible results I thought.
>> Repeating it now on Centos 5.2 and OpenSuSE 10.3, it doesn't behave
>> sensibly, and I don't know what's different from the previous SuSE
>> results apart, probably, from the minor kernel version.  If I set
>> rx-frames=0, I see this:
>>
>> rx-usec    latency (µs)
>> 20         34.6
>> 12         26.3
>> 6          20.0
>> 1          14.8
>>
>> whereas if I just set rx-frames=1, I get 14.7 µs, roughly  
>> independently
>> of rx-usec.  (Those figures are probably ±∼0.2µs.)
>
> That is odd. I have only tested with Intel e1000 and our myri10ge  
> Ethernet driver. The Intel driver does not let you specify value  
> other than certain settings (0, 25, etc.). The myri10ge driver does  
> allow you to specify any value.
>
> Your results may be specific to that driver.

As Patrick kindly pointed out, you are using rx-frames and not rx- 
usec. They are not equivalent.

Scott
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