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@xxxxxxxxxx>
To: "'Kevin D. Kissell'" <kevink@xxxxxxxx>; <linux-mips-bounce@xxxxxxxxxxxxxx>; <linux-mips@xxxxxxxxxxxxxx>
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@xxxxxxxx]
> Sent: Wednesday, January 04, 2006 6:37 PM
> To: Sathesh Babu Edara
> Cc: linux-mips-bounce@xxxxxxxxxxxxxx; linux-mips@xxxxxxxxxxxxxx
> 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.
>
>
>
