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author | Ingo Molnar <mingo@elte.hu> | 2009-06-17 11:06:17 (GMT) |
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committer | Ingo Molnar <mingo@elte.hu> | 2009-06-17 11:06:17 (GMT) |
commit | a3d06cc6aa3e765dc2bf98626f87272dcf641dca (patch) | |
tree | aa3e49b58f08d6c0ea55cdca4fb5e6c8ba6ae333 /include/linux/timex.h | |
parent | 0990b1c65729012a63e0eeca93aaaafea4e9a064 (diff) | |
parent | 65795efbd380a832ae508b04dba8f8e53f0b84d9 (diff) | |
download | linux-fsl-qoriq-a3d06cc6aa3e765dc2bf98626f87272dcf641dca.tar.xz |
Merge branch 'linus' into perfcounters/core
Conflicts:
arch/x86/include/asm/kmap_types.h
include/linux/mm.h
include/asm-generic/kmap_types.h
Merge reason: We crossed changes with kmap_types.h cleanups in mainline.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'include/linux/timex.h')
-rw-r--r-- | include/linux/timex.h | 45 |
1 files changed, 34 insertions, 11 deletions
diff --git a/include/linux/timex.h b/include/linux/timex.h index aa3475f..e6967d1 100644 --- a/include/linux/timex.h +++ b/include/linux/timex.h @@ -170,17 +170,37 @@ struct timex { #include <asm/timex.h> /* - * SHIFT_KG and SHIFT_KF establish the damping of the PLL and are chosen - * for a slightly underdamped convergence characteristic. SHIFT_KH - * establishes the damping of the FLL and is chosen by wisdom and black - * art. + * SHIFT_PLL is used as a dampening factor to define how much we + * adjust the frequency correction for a given offset in PLL mode. + * It also used in dampening the offset correction, to define how + * much of the current value in time_offset we correct for each + * second. Changing this value changes the stiffness of the ntp + * adjustment code. A lower value makes it more flexible, reducing + * NTP convergence time. A higher value makes it stiffer, increasing + * convergence time, but making the clock more stable. * - * MAXTC establishes the maximum time constant of the PLL. With the - * SHIFT_KG and SHIFT_KF values given and a time constant range from - * zero to MAXTC, the PLL will converge in 15 minutes to 16 hours, - * respectively. + * In David Mills' nanokernel reference implementation SHIFT_PLL is 4. + * However this seems to increase convergence time much too long. + * + * https://lists.ntp.org/pipermail/hackers/2008-January/003487.html + * + * In the above mailing list discussion, it seems the value of 4 + * was appropriate for other Unix systems with HZ=100, and that + * SHIFT_PLL should be decreased as HZ increases. However, Linux's + * clock steering implementation is HZ independent. + * + * Through experimentation, a SHIFT_PLL value of 2 was found to allow + * for fast convergence (very similar to the NTPv3 code used prior to + * v2.6.19), with good clock stability. + * + * + * SHIFT_FLL is used as a dampening factor to define how much we + * adjust the frequency correction for a given offset in FLL mode. + * In David Mills' nanokernel reference implementation SHIFT_FLL is 2. + * + * MAXTC establishes the maximum time constant of the PLL. */ -#define SHIFT_PLL 4 /* PLL frequency factor (shift) */ +#define SHIFT_PLL 2 /* PLL frequency factor (shift) */ #define SHIFT_FLL 2 /* FLL frequency factor (shift) */ #define MAXTC 10 /* maximum time constant (shift) */ @@ -192,10 +212,10 @@ struct timex { #define SHIFT_USEC 16 /* frequency offset scale (shift) */ #define PPM_SCALE ((s64)NSEC_PER_USEC << (NTP_SCALE_SHIFT - SHIFT_USEC)) #define PPM_SCALE_INV_SHIFT 19 -#define PPM_SCALE_INV ((1ll << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \ +#define PPM_SCALE_INV ((1LL << (PPM_SCALE_INV_SHIFT + NTP_SCALE_SHIFT)) / \ PPM_SCALE + 1) -#define MAXPHASE 500000000l /* max phase error (ns) */ +#define MAXPHASE 500000000L /* max phase error (ns) */ #define MAXFREQ 500000 /* max frequency error (ns/s) */ #define MAXFREQ_SCALED ((s64)MAXFREQ << NTP_SCALE_SHIFT) #define MINSEC 256 /* min interval between updates (s) */ @@ -260,6 +280,9 @@ extern int do_adjtimex(struct timex *); int read_current_timer(unsigned long *timer_val); +/* The clock frequency of the i8253/i8254 PIT */ +#define PIT_TICK_RATE 1193182ul + #endif /* KERNEL */ #endif /* LINUX_TIMEX_H */ |