asm/timex.h

asm/timex.h

[Vojtech Pavlik]

Hi!

I have several questions about asm/timex.h

1) Who uses it? The kernel certainly doesn't. Perhaps NTP?

2) CLOCK_TICK_RATE is defined on i386 and similar archs
   to be 1193180. This is wrong, because the real frequency
   of the i8253 PIT timer is 14.31818 MHz / 12 = 1.11931816 MHz,
   so CLOCK_TICK_RATE should be 1193182. Should it be fixed?

3) What if an architecture doesn't have a compile-time known
   CLOCK_TICK_RATE? I suppose I cannot just #define it to a variable,
   because the kernel doesn't use it, and that probably means userland
   does ...

Anyone knows the answers?

-- 
Vojtech Pavlik
SuSE Labs

Re: asm/timex.h

[Christoph Hellwig]

On Fri, May 24, 2002 at 07:33:45PM +0200, Vojtech Pavlik wrote:
> Hi!
> 
> I have several questions about asm/timex.h
> 
> 1) Who uses it? The kernel certainly doesn't. Perhaps NTP?

The kernel does.  Thanks to the sched.h mess it's even implictly
included in almost any file..

> 3) What if an architecture doesn't have a compile-time known
>    CLOCK_TICK_RATE? I suppose I cannot just #define it to a variable,
>    because the kernel doesn't use it, and that probably means userland
>    does ...

The kernel DOES use it.  grep(1) is your friend.

Re: asm/timex.h

[Vojtech Pavlik]

On Fri, May 24, 2002 at 06:49:03PM +0100, Christoph Hellwig wrote:
> On Fri, May 24, 2002 at 07:33:45PM +0200, Vojtech Pavlik wrote:
> > Hi!
> > 
> > I have several questions about asm/timex.h
> > 
> > 1) Who uses it? The kernel certainly doesn't. Perhaps NTP?
> 
> The kernel does.  Thanks to the sched.h mess it's even implictly
> included in almost any file..
> 
> > 3) What if an architecture doesn't have a compile-time known
> >    CLOCK_TICK_RATE? I suppose I cannot just #define it to a variable,
> >    because the kernel doesn't use it, and that probably means userland
> >    does ...
> 
> The kernel DOES use it.  grep(1) is your friend.

# grep -rw FINETUNE * | grep -v timex.h
# grep -rw CLOCK_TICK_FACTOR * | grep -v timex.h
# grep -rw CLOCK_TICK_RATE * | grep -v timex.h
drivers/char/ftape/lowlevel/ftape-calibr.c:     return (10000 * count) / ((CLOCK_TICK_RATE + 50) / 100);

The only interesting place where is CLOCK_TICK_RATE used is in linux/timex.h
to define LATCH. Which subsequently is only used in arch specific code
and ftape again.

Ftape's use of it is buggy, because it lacks the needed locking.

So, it seems like CLOCK_TICK_RATE isn't needed by non-arch-specific
code.

And FINETUNE isn't used at all.

But ... the fact that kernel uses it ... probably doesn't mean that
userland doesn't.

-- 
Vojtech Pavlik
SuSE Labs