Remove CLOCK_TICK_RATE from ACTHZ definition

PATCH In review Deepak Saxena 2 participants 2 messages Aug 4, 2011 – Aug 5, 2011

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Deepak Saxena

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2011-08-04 00:08 UTC #0 lore raw

PATCH 1/1 Remove CLOCK_TICK_RATE from ACTHZ definition

As per https://lkml.org/lkml/2011/2/21/323, we remove CLOCK_TICK_RATE from the definition of ACTHZ as the majority of CLOCK_TICK_RATE values are no longer valid or needed for proper operation of the time code.

Signed-off-by Deepak Saxena <[email protected]>

---
 include/linux/jiffies.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

include/linux/jiffies.h +1 -1

index f97672a..d232f00 100644
@@ -55,7 +55,7 @@
                              + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
 
 /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */
-#define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8))
+#define ACTHZ (HZ << 8)
 
 /* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */
 #define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8))

Signature · 1 line

1.7.4.1

john stultz

2011-08-05 10:21 UTC #1 lore raw

Quoted 15 lines · Deepak Saxena

As per https://lkml.org/lkml/2011/2/21/323, we remove CLOCK_TICK_RATE from the definition of ACTHZ as the majority of CLOCK_TICK_RATE values are no longer valid or needed for proper operation of the time code.
Signed-off-by Deepak Saxena <[email protected]>
---
 include/linux/jiffies.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
include/linux/jiffies.h +0 -0
index f97672a..d232f00 100644

include/linux/jiffies.h line 61

Quoted 8 lines

include/linux/jiffies.h +1 -1

@@ -55,7 +55,7 @@
                              + ((((NOM) % (DEN)) << (LSH)) + (DEN) / 2) / (DEN))
 
 /* HZ is the requested value. ACTHZ is actual HZ ("<< 8" is for accuracy) */
-#define ACTHZ (SH_DIV (CLOCK_TICK_RATE, LATCH, 8))
+#define ACTHZ (HZ << 8)
 
 /* TICK_NSEC is the time between ticks in nsec assuming real ACTHZ */
 #define TICK_NSEC (SH_DIV (1000000UL * 1000, ACTHZ, 8))

So I'm hesitant about this patch, since the whole point of ACTHZ is to provide a higher precision value for the actual irq frequency (as hardware won't be able to do exactly 100/250/300/1000HZ).

One could argue that with highres timers, jiffies is usually updated by the timekeeping code, which for the most part isn't affected by irq freq error. So we could reasonably forgo this minor error correction, only hurting systems that use the jiffies clocksource, or require ARCH_USES_GETTIMEOFFSET.

However, we would probably want to kill off all the ACTHZ usage as well since we're at that point gaining nothing from the extra complexity.

thanks
-john