Re: Tweak Latency on Intel ATOM

["Max Müller" <mxmr@gmx.net>]

Clark Williams schrieb:
> On Tue, 9 Feb 2010 07:41:58 +0000 (UTC)
> Max Miller <mxmr@gmx.net> wrote:
>
>   
>> Hello,
>>
>> im am using the PREEMPT-RT patch on linux 2.6.29.6. It runs on a MSI965GSE
>> industial board with Intel ATOM CPU (N270, 1,6GHz) and i945GSE Northbridge. 
>>
>> I got about 45µs as maximum and 13µs as average latency when hyperthreading is
>> disabled. With enabled Hyperthreading the maximum latency increses to about
>> 100µs. I measured the latency with cyclictest. 
>>
>> What can i do to get better maximum latency? Can I do somthing in the kernel
>> configuration or are there some kernel bootoptions? Or is it still impossible
>> with this CPU to get better results?
>>
>> Thanks in advance,
>> Max Miller 
>>
>>
>>     
>
> Make sure you turn off any power management settings in the BIOS and
> turn off the irqbalance and cpuspeed services on the Linux side.
>
> What cyclictest command are you using to measure latency?
>
> Clark
>   

I run cyclictest as follows:

cyclictest -n -t3 -p99

For generating additional system load i run (one to several instances):

while true; do echo "blah" > /dev/null; done &

Then i watch the max. latency from the thread with the highest priority.
Sometimes i add the parameter '-h' to generate a history. In this 
history i can
see that the most latency times are under 20µs, only  about 5ppm are 
worse than 30µs.
Am i doing this correctly?


The only powersave setting in the BIOS is "Intel speedstep" which i 
disabled.


I will check with disabled "irqbalance and cpuspeed services" disabled 
and will report later.


What should the adequate max. latency on this system?





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