Confused about CLOCK_TICK_RATE
Can someone explain CLOCK_TICK_RATE to me? It's defined in arch/powerpc/include/asm/timex.h as such:
#define CLOCK_TICK_RATE 1024000 /* Underlying HZ */
Every architecture defines this, but some use the better comment "Underlying frequency of the HZ timer".
My question is: why is this a constant? Shouldn't it be a variable, perhaps something that is based on tb_ticks_per_usec?
Signature · 2 lines
Timur Tabi Linux kernel developer at Freescale
Quoted 10 lines · Timur Tabi
Can someone explain
CLOCK_TICK_RATEto me? It's defined inarch/powerpc/include/asm/timex.has such:#define
CLOCK_TICK_RATE1024000 /* Underlying HZ */Every architecture defines this, but some use the better comment "Underlying frequency of the HZ timer".
My question is: why is this a constant? Shouldn't it be a variable, perhaps something that is based on
tb_ticks_per_usec?
Looks like legacy crud, originally meant to be the PIT input frequency, that isn't used for much on powerpc. It was probably chosen so as to make HZ == ACTHZ for the supported values of HZ.
-Scott
Quoted 10 lines · Timur Tabi
Can someone explain
CLOCK_TICK_RATEto me? It's defined inarch/powerpc/include/asm/timex.has such:#define
CLOCK_TICK_RATE1024000 /* Underlying HZ */Every architecture defines this, but some use the better comment "Underlying frequency of the HZ timer".
My question is: why is this a constant? Shouldn't it be a variable, perhaps something that is based on
tb_ticks_per_usec?
It's used essentially for making small adjustments to ACTHZ and TICK_NSEC in include/linux/jiffies.h. The value was chosen so that ACTHZ == HZ and TICK_NSEC = 1e9 for all common HZ values, since we can't say at compile time what the decrementer frequency will be. I believe it's all pretty moot since we changed over to using the generic time framework anyway.
Paul.