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SubjectRe: [NEW PATCH] timers, sysctl, signal (only to get POSIX timers and clocks)
Robert de Vries writes:

>> + KERN_CLK_TCK=41, /* int: Ticks per second (clock_t) */
>> There are several HZ values that currently happen to be the same.
>> We have the HZ as seen in /proc, the HZ as seen in the clocks system
>> call, and the HZ as actually used in the kernel for jiffies.
> What's the difference?

Consider what happens if HZ on i386 is increased to 800 HZ for better
response. Currently HZ is seen via /proc, the times() call, and perhaps
some other places. It may be desireable to (at least initially) divide
tick values by 4 when presenting them to userspace. All of them?

Going with separate HZ values provides some flexibility. The network
tools and procps could go to 800 HZ while times() stays at 100 HZ.

>> + KERN_LINUX_COUNTER_HZ=77 /* int: Frequency of free running counter
> */
>> This is a CPU hardware counter? I never would have guessed.
>> CPU_COUNTER_HZ and CPU_TSC_HZ are more descriptive.
> The philosophy is that most processors have some form of counter.
> Not all of them are in the CPU and they are not always called TSC.
> I wanted something generic.

Since "TSC" stands for "Time Stamp Counter", I think it fits well
enough even on non-Intel hardware. Any counter of interest for this
purpose is going to be in the CPU, though it may count at a slower
speed than the processor core is running.

Certainly this isn't a kernel or Linux feature.

> Point taken, are you sure that all platforms can do 64 bit calculations?
> (or does the compiler support it?)

One or the other will handle the problem -- see other mail.

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