On 06/28/2012 01:21 PM, solmac john wrote:

Thanks for reply
what is CONFIG_NO_HZ

Hi!

If you have no idea what a config entry means, use the help in 
menuconfig (or whatever you are using)... e.g. for CONFIG_NO_HZ tells you

----------<snip>--------------
CONFIG_NO_HZ:

  This option enables a tickless system: timer interrupts will
  only trigger on an as-needed basis both when the system is
  busy and when the system is idle.

Symbol: NO_HZ [=n]
Type  : boolean
Prompt: Tickless System (Dynamic Ticks)
    Defined at kernel/time/Kconfig:7
    Depends on: !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS [=y]
    Location:
      -> Processor type and features
    Selects: TICK_ONESHOT [=n]
----------<snap>-------------

So this already gives you a general idea what the config entry does, and 
some other useful info like dependency on other stuff that has to be 
turn on/off.

can we enable CONFIG_NO_HZ and CONFIG_HZ both in our config

This question is also answered here, as "Depends on:" would include 
!CONFIG_HZ_250 if it had to be switched or sth.

and what the drawback of dynamic CONFIG_NO_HZ tick.

I think the problems of longer latencies only apply on idle systems. Not 
100% sure, but I think when the cpu goes into idle, the periodic timer 
is stopped and longer intervals are done using one-shot timer to avoid 
forcing the cpu out of idle just to see that nothing is to do and go 
back into idle.
But I think if the CPU is not in idle the periodic timer.

regards,
andi

On Tue, Jun 26, 2012 at 10:47 AM, Mulyadi Santosa 
<mulyadi.santosa at gmail.com <mailto:mulyadi.santosa@gmail.com>> wrote:

    Hi... :)

    On Tue, Jun 26, 2012 at 12:10 PM, solmac john
    <johnsolmac at gmail.com <mailto:johnsolmac@gmail.com>> wrote:
    > I am using ARM multicore board and by default

    okay, I am answering it from what I know about HZ impact on x86...

    > CONFIG_HZ=250

    looks good... a middle safe number, not too high not too low...

    > Query: - 1- How to decide HZ for particular hardware

    it's you who decide...do you want finer grained timer? or coarse one?

    the impact is usually toward latency and responsiveness....together
    with preemption model you choose actually.

    >               2- Which is the best open source tool to test system
    > performance from given HZ.

    run your application in that platform and see if it gives you impact.
    from my experience, unless you need application that is sensitive in
    timing such as MIDI sequencer, you won't notice the difference.

    --
    regards,

    Mulyadi Santosa
    Freelance Linux trainer and consultant

    blog: the-hydra.blogspot.com <http://the-hydra.blogspot.com/>
    training: mulyaditraining.blogspot.com
    <http://mulyaditraining.blogspot.com/>



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