avoid overflows in kernel/time.c
authorH. Peter Anvin <hpa@zytor.com>
Fri, 8 Feb 2008 12:21:26 +0000 (04:21 -0800)
committerLinus Torvalds <torvalds@woody.linux-foundation.org>
Fri, 8 Feb 2008 17:22:39 +0000 (09:22 -0800)
When the conversion factor between jiffies and milli- or microseconds is
not a single multiply or divide, as for the case of HZ == 300, we currently
do a multiply followed by a divide.  The intervening result, however, is
subject to overflows, especially since the fraction is not simplified (for
HZ == 300, we multiply by 300 and divide by 1000).

This is exposed to the user when passing a large timeout to poll(), for
example.

This patch replaces the multiply-divide with a reciprocal multiplication on
32-bit platforms.  When the input is an unsigned long, there is no portable
way to do this on 64-bit platforms there is no portable way to do this
since it requires a 128-bit intermediate result (which gcc does support on
64-bit platforms but may generate libgcc calls, e.g.  on 64-bit s390), but
since the output is a 32-bit integer in the cases affected, just simplify
the multiply-divide (*3/10 instead of *300/1000).

The reciprocal multiply used can have off-by-one errors in the upper half
of the valid output range.  This could be avoided at the expense of having
to deal with a potential 65-bit intermediate result.  Since the intent is
to avoid overflow problems and most of the other time conversions are only
semiexact, the off-by-one errors were considered an acceptable tradeoff.

At Ralf Baechle's suggestion, this version uses a Perl script to compute
the necessary constants.  We already have dependencies on Perl for kernel
compiles.  This does, however, require the Perl module Math::BigInt, which
is included in the standard Perl distribution starting with version 5.8.0.
In order to support older versions of Perl, include a table of canned
constants in the script itself, and structure the script so that
Math::BigInt isn't required if pulling values from said table.

Running the script requires that the HZ value is available from the
Makefile.  Thus, this patch also adds the Kconfig variable CONFIG_HZ to the
architectures which didn't already have it (alpha, cris, frv, h8300, m32r,
m68k, m68knommu, sparc, v850, and xtensa.) It does *not* touch the sh or
sh64 architectures, since Paul Mundt has dealt with those separately in the
sh tree.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Cc: Ralf Baechle <ralf@linux-mips.org>,
Cc: Sam Ravnborg <sam@ravnborg.org>,
Cc: Paul Mundt <lethal@linux-sh.org>,
Cc: Richard Henderson <rth@twiddle.net>,
Cc: Michael Starvik <starvik@axis.com>,
Cc: David Howells <dhowells@redhat.com>,
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>,
Cc: Hirokazu Takata <takata@linux-m32r.org>,
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Cc: Roman Zippel <zippel@linux-m68k.org>,
Cc: William L. Irwin <sparclinux@vger.kernel.org>,
Cc: Chris Zankel <chris@zankel.net>,
Cc: H. Peter Anvin <hpa@zytor.com>,
Cc: Jan Engelhardt <jengelh@computergmbh.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
29 files changed:
arch/alpha/Kconfig
arch/cris/Kconfig
arch/frv/Kconfig
arch/h8300/Kconfig
arch/m32r/Kconfig
arch/m68k/Kconfig
arch/m68knommu/Kconfig
arch/sparc/Kconfig
arch/v850/Kconfig
arch/xtensa/Kconfig
include/asm-alpha/param.h
include/asm-cris/param.h
include/asm-frv/param.h
include/asm-h8300/param.h
include/asm-m32r/param.h
include/asm-m68k/param.h
include/asm-m68knommu/param.h
include/asm-sparc/param.h
include/asm-v850/anna.h
include/asm-v850/as85ep1.h
include/asm-v850/fpga85e2c.h
include/asm-v850/param.h
include/asm-v850/rte_cb.h
include/asm-v850/sim.h
include/asm-v850/sim85e2.h
include/asm-xtensa/param.h
kernel/Makefile
kernel/time.c
kernel/timeconst.pl [new file with mode: 0644]

index d9df913a464d12421c897dc219016e3fd1749ca8..5b7dcd5a0e75b663e709b093bc2f4f21fb3d49b8 100644 (file)
@@ -615,6 +615,11 @@ config VERBOSE_MCHECK_ON
 
          Take the default (1) unless you want more control or more info.
 
+config HZ
+       int
+       default 1200 if ALPHA_RAWHIDE
+       default 1024
+
 source "drivers/pci/Kconfig"
 source "drivers/eisa/Kconfig"
 
index 27b082ac7f11e25e8d6b292b54af2c932f259217..ff078e60e76da8f2b9ef0753287b8407d44d277f 100644 (file)
@@ -55,6 +55,10 @@ config CRIS
        bool
        default y
 
+config HZ
+       int
+       default 100
+
 source "init/Kconfig"
 
 menu "General setup"
index 96f7d70f4473681dc3f155b31c00215a55267257..9e561ede0925b6928bb44907c1bcde6ee4139d43 100644 (file)
@@ -57,6 +57,10 @@ config ARCH_HAS_ILOG2_U64
        bool
        default y
 
+config HZ
+       int
+       default 1000
+
 mainmenu "Fujitsu FR-V Kernel Configuration"
 
 source "init/Kconfig"
index b4ba4f8b505c2d66f13c906e4a3371efac6bca3e..f69e5ea385588d0c554fe5f0d3ca2ff82f8c2138 100644 (file)
@@ -82,6 +82,10 @@ config PCI
        bool
        default n
 
+config HZ
+       int
+       default 100
+
 source "init/Kconfig"
 
 source "arch/h8300/Kconfig.cpu"
index fe61e00a604f270751b4a4687e93c0297c7bc97a..d4679ab55b969c3fe8bfc4f88dfef02d618e1877 100644 (file)
@@ -38,6 +38,10 @@ config NO_DMA
 config ARCH_SUPPORTS_AOUT
        def_bool y
 
+config HZ
+       int
+       default 100
+
 source "init/Kconfig"
 
 
index bcbf3e4ee9d4c5542eff9116c824f0cf2f983605..2b0ed89cd173728ddda8ad3ea201977c5ee0484c 100644 (file)
@@ -55,6 +55,10 @@ config NO_DMA
 config ARCH_SUPPORTS_AOUT
        def_bool y
 
+config HZ
+       int
+       default 100
+
 mainmenu "Linux/68k Kernel Configuration"
 
 source "init/Kconfig"
index 24f732342d3edca6f31ebd7da4f7d159daac58e8..548a7b321633c670b358f190e2a92a54a694ba45 100644 (file)
@@ -525,6 +525,11 @@ config 4KSTACKS
          running more threads on a system and also reduces the pressure
          on the VM subsystem for higher order allocations.
 
+config HZ
+       int
+       default 1000 if CLEOPATRA
+       default 100
+
 comment "RAM configuration"
 
 config RAMBASE
index 08821b078eccc20a3b4da15359115b5c2ea3990f..7c674a3503b66c8aa2ced1896bc3df6e2a6e7999 100644 (file)
@@ -30,6 +30,10 @@ config OF
 config ARCH_SUPPORTS_AOUT
        def_bool y
 
+config HZ
+       int
+       default 100
+
 source "init/Kconfig"
 
 menu "General machine setup"
index 225f30d7cb32477ca1489412df2c72bfd8eec840..7b6d3716efca4a0f370ef848ac8cecbfa0e39eb6 100644 (file)
@@ -215,6 +215,13 @@ menu "Processor type and features"
          bool
          default !V850E_CACHE && !V850E2_CACHE
 
+   # HZ depends on the platform
+   config HZ
+         int
+         default 24  if V850E_SIM || V850E2_SIM85E2
+         default 122 if V850E2_FPGA85E2C
+         default 100
+
    #### Misc config
 
    config ROM_KERNEL
index 5d5546ce88fe90b02ff376a633a4933b22639685..fd36764d7fb72358a65a3551ad9a0faf7b4a70e1 100644 (file)
@@ -49,6 +49,10 @@ config ARCH_HAS_ILOG2_U64
 config NO_IOPORT
        def_bool y
 
+config HZ
+       int
+       default 100
+
 source "init/Kconfig"
 
 menu "Processor type and features"
index 214e7996346f25e890c9221c35fac975f4e7ee78..0982f1d39499fbe337b440cc995913e2fbbb792d 100644 (file)
@@ -5,15 +5,7 @@
    hardware ignores reprogramming.  We also need userland buy-in to the 
    change in HZ, since this is visible in the wait4 resources etc.  */
 
-
-#ifndef HZ
-# ifndef CONFIG_ALPHA_RAWHIDE
-#  define HZ   1024
-# else
-#  define HZ   1200
-# endif
-#endif
-
+#define HZ             CONFIG_HZ
 #define USER_HZ                HZ
 
 #define EXEC_PAGESIZE  8192
index b249726398320ffcc9b12d56fc227dc3be6929e5..0e47994e40be536de84bcb6ed85a37770fb6015a 100644 (file)
@@ -3,7 +3,7 @@
 
 /* Currently we assume that HZ=100 is good for CRIS. */
 #ifdef __KERNEL__
-# define HZ            100             /* Internal kernel timer frequency */
+# define HZ            CONFIG_HZ       /* Internal kernel timer frequency */
 # define USER_HZ       100             /* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC        (USER_HZ)       /* like times() */
 #endif
index 365653b1726c18892a3a1ea5efb760b50f64ddaa..6859dd503ed366910cfe0fa85e7c0acf53e7f525 100644 (file)
@@ -2,7 +2,7 @@
 #define _ASM_PARAM_H
 
 #ifdef __KERNEL__
-#define HZ             1000            /* Internal kernel timer frequency */
+#define HZ             CONFIG_HZ       /* Internal kernel timer frequency */
 #define USER_HZ                100             /* .. some user interfaces are in "ticks" */
 #define CLOCKS_PER_SEC (USER_HZ)       /* like times() */
 #endif
index c25806ed1fb368d2581b00f853bb4d55ade94b9d..04f64f1003792b77c4a6be5a8da51f3f7b2e9b93 100644 (file)
@@ -3,7 +3,7 @@
 
 
 #ifndef HZ
-#define HZ 100
+#define HZ CONFIG_HZ
 #endif
 
 #ifdef __KERNEL__
index 3e14026e39cdaf2a479d1a09dabaf9c2d6b514b8..94c770196048335767a40f9fd8fd649d11f1effb 100644 (file)
@@ -2,7 +2,7 @@
 #define _ASM_M32R_PARAM_H
 
 #ifdef __KERNEL__
-# define HZ            100             /* Internal kernel timer frequency */
+# define HZ            CONFIG_HZ       /* Internal kernel timer frequency */
 # define USER_HZ       100             /* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC        (USER_HZ)       /* like times() */
 #endif
index 60f409d81658193e36e1f077d1e643a1e390b191..536a27888358d59a15e6f4342513a3fb04ebb3be 100644 (file)
@@ -2,7 +2,7 @@
 #define _M68K_PARAM_H
 
 #ifdef __KERNEL__
-# define HZ            100             /* Internal kernel timer frequency */
+# define HZ            CONFIG_HZ       /* Internal kernel timer frequency */
 # define USER_HZ       100             /* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC        (USER_HZ)       /* like times() */
 #endif
index 4c9904d6512ed6e278184fa56375d072239f0f07..96c45101832491ecbb7e0cabdb5b49d49f5fa5d2 100644 (file)
@@ -1,13 +1,7 @@
 #ifndef _M68KNOMMU_PARAM_H
 #define _M68KNOMMU_PARAM_H
 
-
-#if defined(CONFIG_CLEOPATRA)
-#define        HZ 1000
-#endif
-#ifndef HZ
-#define        HZ 100
-#endif
+#define HZ CONFIG_HZ
 
 #ifdef __KERNEL__
 #define        USER_HZ         HZ
index beaf02d364f231374f0f6c602f68839754b2cec2..86ba59af9d2c7d44d775a64d3c548d53622228a2 100644 (file)
@@ -3,7 +3,7 @@
 #define _ASMSPARC_PARAM_H
 
 #ifdef __KERNEL__
-# define HZ            100     /* Internal kernel timer frequency */
+# define HZ            CONFIG_HZ       /* Internal kernel timer frequency */
 # define USER_HZ       100     /* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC (USER_HZ)
 #endif
index 3be77d5ecfce38c9d9efec628c529582083ef92f..cd5eaee103b0f8069bf3de282cbb4ac9d34ba5ef 100644 (file)
@@ -134,10 +134,4 @@ extern void anna_uart_pre_configure (unsigned chan,
 #define V850E_TIMER_D_TMCD_CS_MIN      1 /* min 2^1 divider */
 
 
-/* For <asm/param.h> */
-#ifndef HZ
-#define HZ     100
-#endif
-
-
 #endif /* __V850_ANNA_H__ */
index 659bc910ffd72f060012131b8c6fc05775e3299c..5a5ca9073d0931027a470091ecec0ac81ceddb4d 100644 (file)
@@ -149,10 +149,4 @@ extern void as85ep1_uart_pre_configure (unsigned chan,
 #define V850E_TIMER_D_TMCD_CS_MIN      2 /* min 2^2 divider */
 
 
-/* For <asm/param.h> */
-#ifndef HZ
-#define HZ     100
-#endif
-
-
 #endif /* __V850_AS85EP1_H__ */
index d32f04504b135073de1410fc14e8ea103184d6a5..23aae666c718ce62ae1f18129d6eec12021a3f5b 100644 (file)
@@ -79,10 +79,4 @@ extern char _r0_ram;
 #endif
 
 
-/* For <asm/param.h> */
-#ifndef HZ
-#define HZ                     122 /* actually, 8.192ms ticks =~ 122.07 */
-#endif
-
-
 #endif /* __V850_FPGA85E2C_H__ */
index 3c65bd573782d34e060d52299bfcc5a4cd7b37bb..281832690290536007c861a8362634cb673b7f43 100644 (file)
@@ -23,8 +23,7 @@
 #define MAXHOSTNAMELEN 64      /* max length of hostname */
 
 #ifdef __KERNEL__
-#include <asm/machdep.h>       /* For HZ */
-
+# define HZ            CONFIG_HZ
 # define USER_HZ       100
 # define CLOCKS_PER_SEC        USER_HZ
 #endif
index e85d261b79bf0ee140ab1f5f349b6b25e100d25d..db9879f00aa7b9adacca1a8b72a7f21126bdbb59 100644 (file)
 #endif /* CONFIG_RTE_MB_A_PCI */
 
 
-/* For <asm/param.h> */
-#ifndef HZ
-#define HZ     100
-#endif
-
-
 #ifndef __ASSEMBLY__
 extern void rte_cb_early_init (void);
 extern void rte_cb_init_irqs (void);
index 10236abbe9be7aca7fdfb04c4f28a1b1d3ee0aad..026932d476cd9036aa57208e780076687f6ba99b 100644 (file)
 #define R0_RAM_ADDR            0xFFFFF000
 
 
-/* For <asm/param.h> */
-#ifndef HZ
-#define HZ                     24      /* Minimum supported frequency.  */
-#endif
-
 /* For <asm/irq.h> */
 #define NUM_CPU_IRQS           6
 
index 17dd4fa318e65d4eb17ecbfb0f824b525f139eeb..8b4d6974066c2d624f3deb58ff32c17e5950682b 100644 (file)
 #define R0_RAM_ADDR            0xFFFFE000
 
 
-/* For <asm/param.h> */
-#ifndef HZ
-#define HZ                     24      /* Minimum supported frequency.  */
-#endif
-
-
 #endif /* __V850_SIM85E2_H__ */
index ce3a336cad07c188ebe7dc10805c2d6c060212a8..82ad34d92d359746de497c9a680306a7a661f45f 100644 (file)
@@ -12,7 +12,7 @@
 #define _XTENSA_PARAM_H
 
 #ifdef __KERNEL__
-# define HZ            100             /* internal timer frequency */
+# define HZ            CONFIG_HZ       /* internal timer frequency */
 # define USER_HZ       100             /* for user interfaces in "ticks" */
 # define CLOCKS_PER_SEC (USER_HZ)      /* frequnzy at which times() counts */
 #endif
index 60cd39c84e6d47bce185e616a10bf790c7becfbb..6c584c55a6e9e8f164fa949b8a5c5ed8054ed9f8 100644 (file)
@@ -91,3 +91,11 @@ quiet_cmd_ikconfiggz = IKCFG   $@
 targets += config_data.h
 $(obj)/config_data.h: $(obj)/config_data.gz FORCE
        $(call if_changed,ikconfiggz)
+
+$(obj)/time.o: $(obj)/timeconst.h
+
+quiet_cmd_timeconst  = TIMEC   $@
+      cmd_timeconst  = $(PERL) $< $(CONFIG_HZ) > $@
+targets += timeconst.h
+$(obj)/timeconst.h: $(src)/timeconst.pl FORCE
+       $(call if_changed,timeconst)
index 3b705ecc3fb7843eff331cbf077f314c22a8f071..a5ec013b6c807be91292179023406e995f765fb2 100644 (file)
@@ -39,6 +39,8 @@
 #include <asm/uaccess.h>
 #include <asm/unistd.h>
 
+#include "timeconst.h"
+
 /*
  * The timezone where the local system is located.  Used as a default by some
  * programs who obtain this value by using gettimeofday.
@@ -93,7 +95,8 @@ asmlinkage long sys_stime(time_t __user *tptr)
 
 #endif /* __ARCH_WANT_SYS_TIME */
 
-asmlinkage long sys_gettimeofday(struct timeval __user *tv, struct timezone __user *tz)
+asmlinkage long sys_gettimeofday(struct timeval __user *tv,
+                                struct timezone __user *tz)
 {
        if (likely(tv != NULL)) {
                struct timeval ktv;
@@ -118,7 +121,7 @@ asmlinkage long sys_gettimeofday(struct timeval __user *tv, struct timezone __us
  * hard to make the program warp the clock precisely n hours)  or
  * compile in the timezone information into the kernel.  Bad, bad....
  *
- *                                             - TYT, 1992-01-01
+ *                                             - TYT, 1992-01-01
  *
  * The best thing to do is to keep the CMOS clock in universal time (UTC)
  * as real UNIX machines always do it. This avoids all headaches about
@@ -240,7 +243,11 @@ unsigned int inline jiffies_to_msecs(const unsigned long j)
 #elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
        return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
 #else
-       return (j * MSEC_PER_SEC) / HZ;
+# if BITS_PER_LONG == 32
+       return ((u64)HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
+# else
+       return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
+# endif
 #endif
 }
 EXPORT_SYMBOL(jiffies_to_msecs);
@@ -252,7 +259,11 @@ unsigned int inline jiffies_to_usecs(const unsigned long j)
 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
        return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
 #else
-       return (j * USEC_PER_SEC) / HZ;
+# if BITS_PER_LONG == 32
+       return ((u64)HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
+# else
+       return (j * HZ_TO_USEC_NUM) / HZ_TO_USEC_DEN;
+# endif
 #endif
 }
 EXPORT_SYMBOL(jiffies_to_usecs);
@@ -352,7 +363,7 @@ EXPORT_SYMBOL(mktime);
  * normalize to the timespec storage format
  *
  * Note: The tv_nsec part is always in the range of
- *     0 <= tv_nsec < NSEC_PER_SEC
+ *     0 <= tv_nsec < NSEC_PER_SEC
  * For negative values only the tv_sec field is negative !
  */
 void set_normalized_timespec(struct timespec *ts, time_t sec, long nsec)
@@ -453,12 +464,13 @@ unsigned long msecs_to_jiffies(const unsigned int m)
        /*
         * Generic case - multiply, round and divide. But first
         * check that if we are doing a net multiplication, that
-        * we wouldnt overflow:
+        * we wouldn't overflow:
         */
        if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
                return MAX_JIFFY_OFFSET;
 
-       return (m * HZ + MSEC_PER_SEC - 1) / MSEC_PER_SEC;
+       return ((u64)MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
+               >> MSEC_TO_HZ_SHR32;
 #endif
 }
 EXPORT_SYMBOL(msecs_to_jiffies);
@@ -472,7 +484,8 @@ unsigned long usecs_to_jiffies(const unsigned int u)
 #elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
        return u * (HZ / USEC_PER_SEC);
 #else
-       return (u * HZ + USEC_PER_SEC - 1) / USEC_PER_SEC;
+       return ((u64)USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
+               >> USEC_TO_HZ_SHR32;
 #endif
 }
 EXPORT_SYMBOL(usecs_to_jiffies);
diff --git a/kernel/timeconst.pl b/kernel/timeconst.pl
new file mode 100644 (file)
index 0000000..62b1287
--- /dev/null
@@ -0,0 +1,402 @@
+#!/usr/bin/perl
+# -----------------------------------------------------------------------
+#
+#   Copyright 2007 rPath, Inc. - All Rights Reserved
+#
+#   This file is part of the Linux kernel, and is made available under
+#   the terms of the GNU General Public License version 2 or (at your
+#   option) any later version; incorporated herein by reference.
+#
+# -----------------------------------------------------------------------
+#
+
+#
+# Usage: timeconst.pl HZ > timeconst.h
+#
+
+# Precomputed values for systems without Math::BigInt
+# Generated by:
+# timeconst.pl --can 24 32 48 64 100 122 128 200 250 256 300 512 1000 1024 1200
+%canned_values = (
+       24 => [
+               '0xa6aaaaab','0x2aaaaaa',26,
+               '0xa6aaaaaaaaaaaaab','0x2aaaaaaaaaaaaaa',58,
+               125,3,
+               '0xc49ba5e4','0x1fbe76c8b4',37,
+               '0xc49ba5e353f7ceda','0x1fbe76c8b439581062',69,
+               3,125,
+               '0xa2c2aaab','0xaaaa',16,
+               '0xa2c2aaaaaaaaaaab','0xaaaaaaaaaaaa',48,
+               125000,3,
+               '0xc9539b89','0x7fffbce4217d',47,
+               '0xc9539b8887229e91','0x7fffbce4217d2849cb25',79,
+               3,125000,
+       ], 32 => [
+               '0xfa000000','0x6000000',27,
+               '0xfa00000000000000','0x600000000000000',59,
+               125,4,
+               '0x83126e98','0xfdf3b645a',36,
+               '0x83126e978d4fdf3c','0xfdf3b645a1cac0831',68,
+               4,125,
+               '0xf4240000','0x0',17,
+               '0xf424000000000000','0x0',49,
+               31250,1,
+               '0x8637bd06','0x3fff79c842fa',46,
+               '0x8637bd05af6c69b6','0x3fff79c842fa5093964a',78,
+               1,31250,
+       ], 48 => [
+               '0xa6aaaaab','0x6aaaaaa',27,
+               '0xa6aaaaaaaaaaaaab','0x6aaaaaaaaaaaaaa',59,
+               125,6,
+               '0xc49ba5e4','0xfdf3b645a',36,
+               '0xc49ba5e353f7ceda','0xfdf3b645a1cac0831',68,
+               6,125,
+               '0xa2c2aaab','0x15555',17,
+               '0xa2c2aaaaaaaaaaab','0x1555555555555',49,
+               62500,3,
+               '0xc9539b89','0x3fffbce4217d',46,
+               '0xc9539b8887229e91','0x3fffbce4217d2849cb25',78,
+               3,62500,
+       ], 64 => [
+               '0xfa000000','0xe000000',28,
+               '0xfa00000000000000','0xe00000000000000',60,
+               125,8,
+               '0x83126e98','0x7ef9db22d',35,
+               '0x83126e978d4fdf3c','0x7ef9db22d0e560418',67,
+               8,125,
+               '0xf4240000','0x0',18,
+               '0xf424000000000000','0x0',50,
+               15625,1,
+               '0x8637bd06','0x1fff79c842fa',45,
+               '0x8637bd05af6c69b6','0x1fff79c842fa5093964a',77,
+               1,15625,
+       ], 100 => [
+               '0xa0000000','0x0',28,
+               '0xa000000000000000','0x0',60,
+               10,1,
+               '0xcccccccd','0x733333333',35,
+               '0xcccccccccccccccd','0x73333333333333333',67,
+               1,10,
+               '0x9c400000','0x0',18,
+               '0x9c40000000000000','0x0',50,
+               10000,1,
+               '0xd1b71759','0x1fff2e48e8a7',45,
+               '0xd1b71758e219652c','0x1fff2e48e8a71de69ad4',77,
+               1,10000,
+       ], 122 => [
+               '0x8325c53f','0xfbcda3a',28,
+               '0x8325c53ef368eb05','0xfbcda3ac10c9714',60,
+               500,61,
+               '0xf9db22d1','0x7fbe76c8b',35,
+               '0xf9db22d0e560418a','0x7fbe76c8b43958106',67,
+               61,500,
+               '0x8012e2a0','0x3ef36',18,
+               '0x8012e29f79b47583','0x3ef368eb04325',50,
+               500000,61,
+               '0xffda4053','0x1ffffbce4217',45,
+               '0xffda4052d666a983','0x1ffffbce4217d2849cb2',77,
+               61,500000,
+       ], 128 => [
+               '0xfa000000','0x1e000000',29,
+               '0xfa00000000000000','0x1e00000000000000',61,
+               125,16,
+               '0x83126e98','0x3f7ced916',34,
+               '0x83126e978d4fdf3c','0x3f7ced916872b020c',66,
+               16,125,
+               '0xf4240000','0x40000',19,
+               '0xf424000000000000','0x4000000000000',51,
+               15625,2,
+               '0x8637bd06','0xfffbce4217d',44,
+               '0x8637bd05af6c69b6','0xfffbce4217d2849cb25',76,
+               2,15625,
+       ], 200 => [
+               '0xa0000000','0x0',29,
+               '0xa000000000000000','0x0',61,
+               5,1,
+               '0xcccccccd','0x333333333',34,
+               '0xcccccccccccccccd','0x33333333333333333',66,
+               1,5,
+               '0x9c400000','0x0',19,
+               '0x9c40000000000000','0x0',51,
+               5000,1,
+               '0xd1b71759','0xfff2e48e8a7',44,
+               '0xd1b71758e219652c','0xfff2e48e8a71de69ad4',76,
+               1,5000,
+       ], 250 => [
+               '0x80000000','0x0',29,
+               '0x8000000000000000','0x0',61,
+               4,1,
+               '0x80000000','0x180000000',33,
+               '0x8000000000000000','0x18000000000000000',65,
+               1,4,
+               '0xfa000000','0x0',20,
+               '0xfa00000000000000','0x0',52,
+               4000,1,
+               '0x83126e98','0x7ff7ced9168',43,
+               '0x83126e978d4fdf3c','0x7ff7ced916872b020c4',75,
+               1,4000,
+       ], 256 => [
+               '0xfa000000','0x3e000000',30,
+               '0xfa00000000000000','0x3e00000000000000',62,
+               125,32,
+               '0x83126e98','0x1fbe76c8b',33,
+               '0x83126e978d4fdf3c','0x1fbe76c8b43958106',65,
+               32,125,
+               '0xf4240000','0xc0000',20,
+               '0xf424000000000000','0xc000000000000',52,
+               15625,4,
+               '0x8637bd06','0x7ffde7210be',43,
+               '0x8637bd05af6c69b6','0x7ffde7210be9424e592',75,
+               4,15625,
+       ], 300 => [
+               '0xd5555556','0x2aaaaaaa',30,
+               '0xd555555555555556','0x2aaaaaaaaaaaaaaa',62,
+               10,3,
+               '0x9999999a','0x1cccccccc',33,
+               '0x999999999999999a','0x1cccccccccccccccc',65,
+               3,10,
+               '0xd0555556','0xaaaaa',20,
+               '0xd055555555555556','0xaaaaaaaaaaaaa',52,
+               10000,3,
+               '0x9d495183','0x7ffcb923a29',43,
+               '0x9d495182a9930be1','0x7ffcb923a29c779a6b5',75,
+               3,10000,
+       ], 512 => [
+               '0xfa000000','0x7e000000',31,
+               '0xfa00000000000000','0x7e00000000000000',63,
+               125,64,
+               '0x83126e98','0xfdf3b645',32,
+               '0x83126e978d4fdf3c','0xfdf3b645a1cac083',64,
+               64,125,
+               '0xf4240000','0x1c0000',21,
+               '0xf424000000000000','0x1c000000000000',53,
+               15625,8,
+               '0x8637bd06','0x3ffef39085f',42,
+               '0x8637bd05af6c69b6','0x3ffef39085f4a1272c9',74,
+               8,15625,
+       ], 1000 => [
+               '0x80000000','0x0',31,
+               '0x8000000000000000','0x0',63,
+               1,1,
+               '0x80000000','0x0',31,
+               '0x8000000000000000','0x0',63,
+               1,1,
+               '0xfa000000','0x0',22,
+               '0xfa00000000000000','0x0',54,
+               1000,1,
+               '0x83126e98','0x1ff7ced9168',41,
+               '0x83126e978d4fdf3c','0x1ff7ced916872b020c4',73,
+               1,1000,
+       ], 1024 => [
+               '0xfa000000','0xfe000000',32,
+               '0xfa00000000000000','0xfe00000000000000',64,
+               125,128,
+               '0x83126e98','0x7ef9db22',31,
+               '0x83126e978d4fdf3c','0x7ef9db22d0e56041',63,
+               128,125,
+               '0xf4240000','0x3c0000',22,
+               '0xf424000000000000','0x3c000000000000',54,
+               15625,16,
+               '0x8637bd06','0x1fff79c842f',41,
+               '0x8637bd05af6c69b6','0x1fff79c842fa5093964',73,
+               16,15625,
+       ], 1200 => [
+               '0xd5555556','0xd5555555',32,
+               '0xd555555555555556','0xd555555555555555',64,
+               5,6,
+               '0x9999999a','0x66666666',31,
+               '0x999999999999999a','0x6666666666666666',63,
+               6,5,
+               '0xd0555556','0x2aaaaa',22,
+               '0xd055555555555556','0x2aaaaaaaaaaaaa',54,
+               2500,3,
+               '0x9d495183','0x1ffcb923a29',41,
+               '0x9d495182a9930be1','0x1ffcb923a29c779a6b5',73,
+               3,2500,
+       ]
+);
+
+$has_bigint = eval 'use Math::BigInt qw(bgcd); 1;';
+
+sub bint($)
+{
+       my($x) = @_;
+       return Math::BigInt->new($x);
+}
+
+#
+# Constants for division by reciprocal multiplication.
+# (bits, numerator, denominator)
+#
+sub fmul($$$)
+{
+       my ($b,$n,$d) = @_;
+
+       $n = bint($n);
+       $d = bint($d);
+
+       return scalar (($n << $b)+$d-bint(1))/$d;
+}
+
+sub fadj($$$)
+{
+       my($b,$n,$d) = @_;
+
+       $n = bint($n);
+       $d = bint($d);
+
+       $d = $d/bgcd($n, $d);
+       return scalar (($d-bint(1)) << $b)/$d;
+}
+
+sub fmuls($$$) {
+       my($b,$n,$d) = @_;
+       my($s,$m);
+       my($thres) = bint(1) << ($b-1);
+
+       $n = bint($n);
+       $d = bint($d);
+
+       for ($s = 0; 1; $s++) {
+               $m = fmul($s,$n,$d);
+               return $s if ($m >= $thres);
+       }
+       return 0;
+}
+
+# Provides mul, adj, and shr factors for a specific
+# (bit, time, hz) combination
+sub muladj($$$) {
+       my($b, $t, $hz) = @_;
+       my $s = fmuls($b, $t, $hz);
+       my $m = fmul($s, $t, $hz);
+       my $a = fadj($s, $t, $hz);
+       return ($m->as_hex(), $a->as_hex(), $s);
+}
+
+# Provides numerator, denominator values
+sub numden($$) {
+       my($n, $d) = @_;
+       my $g = bgcd($n, $d);
+       return ($n/$g, $d/$g);
+}
+
+# All values for a specific (time, hz) combo
+sub conversions($$) {
+       my ($t, $hz) = @_;
+       my @val = ();
+
+       # HZ_TO_xx
+       push(@val, muladj(32, $t, $hz));
+       push(@val, muladj(64, $t, $hz));
+       push(@val, numden($t, $hz));
+
+       # xx_TO_HZ
+       push(@val, muladj(32, $hz, $t));
+       push(@val, muladj(64, $hz, $t));
+       push(@val, numden($hz, $t));
+
+       return @val;
+}
+
+sub compute_values($) {
+       my($hz) = @_;
+       my @val = ();
+       my $s, $m, $a, $g;
+
+       if (!$has_bigint) {
+               die "$0: HZ == $hz not canned and ".
+                   "Math::BigInt not available\n";
+       }
+
+       # MSEC conversions
+       push(@val, conversions(1000, $hz));
+
+       # USEC conversions
+       push(@val, conversions(1000000, $hz));
+
+       return @val;
+}
+
+sub output($@)
+{
+       my($hz, @val) = @_;
+       my $pfx, $bit, $suf, $s, $m, $a;
+
+       print "/* Automatically generated by kernel/timeconst.pl */\n";
+       print "/* Conversion constants for HZ == $hz */\n";
+       print "\n";
+       print "#ifndef KERNEL_TIMECONST_H\n";
+       print "#define KERNEL_TIMECONST_H\n";
+       print "\n";
+
+       print "#include <linux/param.h>\n";
+
+       print "\n";
+       print "#if HZ != $hz\n";
+       print "#error \"kernel/timeconst.h has the wrong HZ value!\"\n";
+       print "#endif\n";
+       print "\n";
+
+       foreach $pfx ('HZ_TO_MSEC','MSEC_TO_HZ',
+                     'USEC_TO_HZ','HZ_TO_USEC') {
+               foreach $bit (32, 64) {
+                       foreach $suf ('MUL', 'ADJ', 'SHR') {
+                               printf "#define %-23s %s\n",
+                                       "${pfx}_$suf$bit", shift(@val);
+                       }
+               }
+               foreach $suf ('NUM', 'DEN') {
+                       printf "#define %-23s %s\n",
+                               "${pfx}_$suf", shift(@val);
+               }
+       }
+
+       print "\n";
+       print "#endif /* KERNEL_TIMECONST_H */\n";
+}
+
+($hz) = @ARGV;
+
+# Use this to generate the %canned_values structure
+if ($hz eq '--can') {
+       shift(@ARGV);
+       @hzlist = sort {$a <=> $b} (@ARGV);
+
+       print "# Precomputed values for systems without Math::BigInt\n";
+       print "# Generated by:\n";
+       print "# timeconst.pl --can ", join(' ', @hzlist), "\n";
+       print "\%canned_values = (\n";
+       my $pf = "\t";
+       foreach $hz (@hzlist) {
+               my @values = compute_values($hz);
+               print "$pf$hz => [\n";
+               while (scalar(@values)) {
+                       my $bit;
+                       foreach $bit (32, 64) {
+                               my $m = shift(@values);
+                               my $a = shift(@values);
+                               my $s = shift(@values);
+                               print "\t\t\'",$m,"\',\'",$a,"\',",$s,",\n";
+                       }
+                       my $n = shift(@values);
+                       my $d = shift(@values);
+                       print "\t\t",$n,',',$d,",\n";
+               }
+               print "\t]";
+               $pf = ', ';
+       }
+       print "\n);\n";
+} else {
+       $hz += 0;                       # Force to number
+       if ($hz < 1) {
+               die "Usage: $0 HZ\n";
+       }
+
+       @val = @{$canned_values{$hz}};
+       if (!defined(@val)) {
+               @val = compute_values($hz);
+       }
+       output($hz, @val);
+}
+exit 0;