Re: Query regarding 2.6.335 RT and Non-RT performance

[Sven-Thorsten Dietrich <thebigcorporation@gmail.com>]

On Thu, 2010-08-19 at 07:59 -0700, Nivedita Singhvi wrote:
> On 08/17/2010 03:22 PM, Manikandan Ramachandran wrote:
> 
> 
> > I see a scenario where higher priority task is ready to run but lower
> > priority IRQ thread is hogging the cpu. Please see the timeline log
> > below:
> >
> > GIVE ffff0c1c [Comment: High priority IRQ thread wakes up high
> > priority process at jiffy 0xffff0c1c]
> > **ffff0c21**##ffff0c21##**ffff0c21**##ffff0c21##**ffff0c21**##ffff0c21##**ffff0c21**##ffff0c21##**ffff0c21**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c22**##ffff0c22##**ffff0c23**##ffff0c23##**ffff0c23**##ffff0c23##**ffff0c23**##ffff0c24##**ffff0c24**##ffff0c24##**ffff0c24**##ffff0c24##
> > [Comment: Low priority IDE[ide_intr] handler hogs CPU for almost 3 ms]
> > GOTffff0c26 [Comment: High priority task wakes up after 10 ms!!]
> >
> > I fail to understand why scheduler failed to schedule high priority
> > task 10 times in a row. FYI, I have put IDE thread to SCHED_NORMAL
> > while high priority thread and task to SCHED_FIFO.
> 
> Not really sure from the above what's going on, what priorities
> you are running at, etc.
> 
> You might want look at the output of "ps -eLo pid,rtprio,policy,comm"
> to see if you can confirm your scheduler attributes.
> 

Also, use the tracing facilities, as its hard to understand your time
line and the source of it.

I think if your priorities are right, your kernel config is right, and
your measurement tool doesn't interfere, 10 ms latency is incredibly
unlikely.


> thanks,
> Nivedita
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