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![David Fries](/assets/img/avatar_default.png)
The kernel has a divide by zero crash when trying to run the system timer less than 100Hz. The problem is x/(HZ/USER_HZ) and related. Now x*(USER_HZ/HZ) will be used if HZ<USER_HZ. I'm running the Linux kernel under qemu and went to run a slower system timer to take less CPU (and battery) on the host. I found that the kernel paniced under emulation because of a divide by zero in three places. Here is the patch. The base git was updated today 01-05-2008. I went for a 20Hz system time by adding config HZ_20 etc to kernel/Kconfig.hz. With this patch I verified the system timer by looking at /proc/interrupts. [akpm@linux-foundation.org: partially clean up the macro maze] Signed-off-by: David Fries <david@fries.net> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
210 lines
5.7 KiB
C
210 lines
5.7 KiB
C
/*
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* BSD Process Accounting for Linux - Definitions
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*
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* Author: Marco van Wieringen (mvw@planets.elm.net)
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*
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* This header file contains the definitions needed to implement
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* BSD-style process accounting. The kernel accounting code and all
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* user-level programs that try to do something useful with the
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* process accounting log must include this file.
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*
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* Copyright (C) 1995 - 1997 Marco van Wieringen - ELM Consultancy B.V.
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*
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*/
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#ifndef _LINUX_ACCT_H
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#define _LINUX_ACCT_H
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#include <linux/types.h>
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#include <asm/param.h>
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#include <asm/byteorder.h>
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/*
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* comp_t is a 16-bit "floating" point number with a 3-bit base 8
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* exponent and a 13-bit fraction.
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* comp2_t is 24-bit with 5-bit base 2 exponent and 20 bit fraction
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* (leading 1 not stored).
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* See linux/kernel/acct.c for the specific encoding systems used.
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*/
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typedef __u16 comp_t;
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typedef __u32 comp2_t;
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/*
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* accounting file record
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*
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* This structure contains all of the information written out to the
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* process accounting file whenever a process exits.
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*/
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#define ACCT_COMM 16
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struct acct
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{
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char ac_flag; /* Flags */
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char ac_version; /* Always set to ACCT_VERSION */
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/* for binary compatibility back until 2.0 */
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__u16 ac_uid16; /* LSB of Real User ID */
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__u16 ac_gid16; /* LSB of Real Group ID */
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__u16 ac_tty; /* Control Terminal */
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__u32 ac_btime; /* Process Creation Time */
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comp_t ac_utime; /* User Time */
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comp_t ac_stime; /* System Time */
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comp_t ac_etime; /* Elapsed Time */
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comp_t ac_mem; /* Average Memory Usage */
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comp_t ac_io; /* Chars Transferred */
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comp_t ac_rw; /* Blocks Read or Written */
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comp_t ac_minflt; /* Minor Pagefaults */
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comp_t ac_majflt; /* Major Pagefaults */
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comp_t ac_swaps; /* Number of Swaps */
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/* m68k had no padding here. */
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#if !defined(CONFIG_M68K) || !defined(__KERNEL__)
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__u16 ac_ahz; /* AHZ */
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#endif
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__u32 ac_exitcode; /* Exitcode */
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char ac_comm[ACCT_COMM + 1]; /* Command Name */
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__u8 ac_etime_hi; /* Elapsed Time MSB */
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__u16 ac_etime_lo; /* Elapsed Time LSB */
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__u32 ac_uid; /* Real User ID */
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__u32 ac_gid; /* Real Group ID */
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};
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struct acct_v3
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{
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char ac_flag; /* Flags */
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char ac_version; /* Always set to ACCT_VERSION */
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__u16 ac_tty; /* Control Terminal */
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__u32 ac_exitcode; /* Exitcode */
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__u32 ac_uid; /* Real User ID */
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__u32 ac_gid; /* Real Group ID */
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__u32 ac_pid; /* Process ID */
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__u32 ac_ppid; /* Parent Process ID */
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__u32 ac_btime; /* Process Creation Time */
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#ifdef __KERNEL__
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__u32 ac_etime; /* Elapsed Time */
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#else
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float ac_etime; /* Elapsed Time */
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#endif
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comp_t ac_utime; /* User Time */
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comp_t ac_stime; /* System Time */
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comp_t ac_mem; /* Average Memory Usage */
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comp_t ac_io; /* Chars Transferred */
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comp_t ac_rw; /* Blocks Read or Written */
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comp_t ac_minflt; /* Minor Pagefaults */
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comp_t ac_majflt; /* Major Pagefaults */
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comp_t ac_swaps; /* Number of Swaps */
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char ac_comm[ACCT_COMM]; /* Command Name */
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};
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/*
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* accounting flags
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*/
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/* bit set when the process ... */
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#define AFORK 0x01 /* ... executed fork, but did not exec */
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#define ASU 0x02 /* ... used super-user privileges */
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#define ACOMPAT 0x04 /* ... used compatibility mode (VAX only not used) */
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#define ACORE 0x08 /* ... dumped core */
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#define AXSIG 0x10 /* ... was killed by a signal */
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#ifdef __BIG_ENDIAN
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#define ACCT_BYTEORDER 0x80 /* accounting file is big endian */
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#else
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#define ACCT_BYTEORDER 0x00 /* accounting file is little endian */
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#endif
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#ifdef __KERNEL__
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#ifdef CONFIG_BSD_PROCESS_ACCT
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struct vfsmount;
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struct super_block;
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struct pacct_struct;
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extern void acct_auto_close_mnt(struct vfsmount *m);
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extern void acct_auto_close(struct super_block *sb);
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extern void acct_init_pacct(struct pacct_struct *pacct);
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extern void acct_collect(long exitcode, int group_dead);
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extern void acct_process(void);
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#else
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#define acct_auto_close_mnt(x) do { } while (0)
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#define acct_auto_close(x) do { } while (0)
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#define acct_init_pacct(x) do { } while (0)
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#define acct_collect(x,y) do { } while (0)
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#define acct_process() do { } while (0)
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#endif
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/*
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* ACCT_VERSION numbers as yet defined:
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* 0: old format (until 2.6.7) with 16 bit uid/gid
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* 1: extended variant (binary compatible on M68K)
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* 2: extended variant (binary compatible on everything except M68K)
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* 3: new binary incompatible format (64 bytes)
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* 4: new binary incompatible format (128 bytes)
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* 5: new binary incompatible format (128 bytes, second half)
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*
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*/
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#ifdef CONFIG_BSD_PROCESS_ACCT_V3
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#define ACCT_VERSION 3
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#define AHZ 100
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typedef struct acct_v3 acct_t;
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#else
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#ifdef CONFIG_M68K
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#define ACCT_VERSION 1
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#else
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#define ACCT_VERSION 2
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#endif
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#define AHZ (USER_HZ)
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typedef struct acct acct_t;
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#endif
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#else
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#define ACCT_VERSION 2
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#define AHZ (HZ)
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#endif /* __KERNEL */
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#ifdef __KERNEL__
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#include <linux/jiffies.h>
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/*
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* Yet another set of HZ to *HZ helper functions.
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* See <linux/jiffies.h> for the original.
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*/
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static inline u32 jiffies_to_AHZ(unsigned long x)
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{
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#if (TICK_NSEC % (NSEC_PER_SEC / AHZ)) == 0
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# if HZ < AHZ
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return x * (AHZ / HZ);
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# else
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return x / (HZ / AHZ);
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# endif
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#else
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u64 tmp = (u64)x * TICK_NSEC;
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do_div(tmp, (NSEC_PER_SEC / AHZ));
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return (long)tmp;
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#endif
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}
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static inline u64 nsec_to_AHZ(u64 x)
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{
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#if (NSEC_PER_SEC % AHZ) == 0
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do_div(x, (NSEC_PER_SEC / AHZ));
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#elif (AHZ % 512) == 0
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x *= AHZ/512;
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do_div(x, (NSEC_PER_SEC / 512));
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#else
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/*
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* max relative error 5.7e-8 (1.8s per year) for AHZ <= 1024,
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* overflow after 64.99 years.
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* exact for AHZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
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*/
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x *= 9;
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do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (AHZ/2))
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/ AHZ));
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#endif
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return x;
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}
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#endif /* __KERNEL */
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#endif /* _LINUX_ACCT_H */
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