Query regarding 2.6.335 RT[Ingo's] and Non-RT performance

[Xianghua Xiao]

On Thu, Aug 12, 2010 at 12:53 PM, Jeff Angielski <jeff at theptrgroup.com> wrote:
> On 08/11/2010 06:18 PM, Manikandan Ramachandran wrote:
>>
>> Hello All,
>>     I created a very simple program which has higher priority than
>> normal tasks and runs a tight loop. Under same test environment I ran
>> this program on both non-rt and rt 2.6.33.5 kernel.  To my suprise I see
>> that performance of non-RT kernel is better than RT. non-RT kernel took
>> 3 sec and 366156 usec while RT kernel took about 3 sec and 418011
>> usec.Can someone please explain why the performance of non-rt kernel is
>> better than rt kernel? From the face of the test result, I feel RT has
>> more overhead,Is there any configuration that I could do to bring down
>> the overhead?
>
> Your "surprise" is due to your definition of "performance".
>
> The purpose of the -rt kernels is to reduce the kernel latency.  This is
> important for servicing hardware.  Normal users find the -rt useful for
> audio/video applications.  Engineering and scientific users find the -rt
> beneficially for servicing hardware like sensors or control systems.
>
> If you are just trying to run calculations as fast as you can in user space,
> you'd be better off using the non-rt variants.
>
>
> --
> Jeff Angielski
> The PTR Group
> www.theptrgroup.com
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>

true, in most cases non-rt will have better performance/throughput,
while rt's major goal is to have better latency for high priority
tasks. also true is that, rt kernel will have more overhead.

xianghua