Re: Query regarding 2.6.335 RT and Non-RT performance

[Nivedita Singhvi <niv@us.ibm.com>]

On 08/17/2010 11:24 AM, Manikandan Ramachandran wrote:

> Thanks David&  Mark for your valuable input!
>
> I'm not expecting RT kernel to be real fast. However I expect latency
> of higher priority task to be less in RT kernel. I'll run the tests
> that you have suggested and see if there is any inherent issue with my
> system.

Actually, a more accurate statement would be "I expect max latency
of higher priority task to be less in RT kernel."

This is true for max latency as reported by you (max, min):

Stock:	418011us	3s
RT:	366156us	3s

So while the min might reflect the best that the system can do, the
max does seem a tad high -- you do need to look into that.

> One more query, with RT patch is it possible for higher priority task
> to preempt a lower priority IRQ thread [For eg, IDE] ? If so when does
> that happen, during next timer interrupt [Assuming IRQ thread uses
> whole schedule slot and doesn't yield between]?

Yes, and when that higher priority task becomes runnable.

thanks,
Nivedita