Messages in this thread | | | Date | Tue, 16 Apr 2002 08:42:28 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | RE: Why HZ on i386 is 100 ? |
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On Tue, 16 Apr 2002, BALBIR SINGH wrote:
> I remember seeing somewhere unix system VII used to have HZ set to 60 > for the machines built in the 70's. I wonder if todays pentium iiis and ivs > should still use HZ of 100, though their internal clock is in GHz. >
A different clock goes to the timer chip. It is always:
CLOCK_TICK_RATE 1193180 Hz unless an Elan SC-520 at which time the frequency is: CLOCK_TICK_RATE 1189200 Hz
(from ../include/asm/timex.h)
> I think somethings in the kernel may be tuned for the value of HZ, these > things would be arch specific. > > Increasing the HZ on your system should change the scheduling behaviour, > it could lead to more aggresive scheduling and could affect the > behaviour of the VM subsystem if scheduling happens more frequently. I am > just guessing, I do not know. >
It doesn't/can't change scheduling behavior. It changes only the rate at which a CPU bound task will get the CPU taken away. It also changes the rate it which it gets it back, in a 1:1 ratio, with a net effect of nothing-gained/nothing-lost except for preemption overhead.
> Changing though trivial would require a good look at all the code that > uses HZ. >
The reference to HZ seems to be correct in all the headers so changing it is trivial.
Cheers, Dick Johnson
Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
Windows-2000/Professional isn't.
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