Re:

["Kevin D. Kissell" <kevink@mips.com>]

There is no "ideal" value for a given processor frequency.
The lower the value, the less interrupt processing overhead,
but the slower the response time to events that are detected
or serviced during clock interrupts. 1000 HZ *may* be a sensible
value (I have my doubts, personally) for 2+ GHz PC processors, 
but it's excessive (IMHO) for a 200MHz processor and unworkable 
for a 20MHz CPU. I think that 100HZ is still a reasonable value
for an embedded RISC CPU, but the "ideal" value is going to
be a function of the application.

        Regards,

        Kevin K.

----- Original Message ----- 
From: "Sathesh Babu Edara" <satheshbabu.edara@analog.com>
To: "'Kevin D. Kissell'" <kevink@mips.com>; <linux-mips-bounce@linux-mips.org>; <linux-mips@linux-mips.org>
Sent: Monday, January 09, 2006 8:43 AM
Subject: RE: 


> 
> Hi,
>   Appreciate your response .
> 
>   What is the ideal HZ value if the processor speed is 200Mhz?.
> 
> Regards,
> Sathesh
> -----Original Message-----
> From: Kevin D. Kissell [mailto:kevink@mips.com] 
> Sent: Wednesday, January 04, 2006 6:37 PM
> To: Sathesh Babu Edara
> Cc: linux-mips-bounce@linux-mips.org; linux-mips@linux-mips.org
> Subject: Re: 
> 
> Sathesh Babu Edara wrote:
> >  
> > 
> > Hi,
> >    We have ported linux-2.6.12 kernel onto MIPS processor (LX4189) and 
> > the processor speed is 200Mhz.
> > By default Linux-2.6.12 kernel comes with HZ value 1000.Will this HZ 
> > value cause an overhead on the 200MHZ CPU.Can someone advise me on 
> > whether going back to HZ vaule of 100 like Linux-2.4 will reduce the 
> > overhead on this CPU.What are the side effects this change can cause?.
> 
> The 1000Hz clock should not actually cause any problems with a 200MHz CPU,
> but it will suck up an annoyingly high percentage of available cycles.
> Backing off to 100Hz may cause some degradation of some
> real-time/interactive response times, but the improved overall performance
> will probably more than make up for it.  I never build with a HZ value
> greater than 100 these days, but then again, I'm mostly running on FPGAs and
> other hardware emulators where the CPU clock frequencies may be less than
> 1MHz, and are never more than 33MHz.
> Note that a HZ  value of less than 100 may cause some kernel macros to
> generate divide-by-zero operations/exceptions.
> 
> Regards,
> 
> Kevin K.
> 
> 
>