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Date: Tue, 26 Feb 2008 02:55:56 +0100 (CET)
From: Roman Zippel <zippel@...ux-m68k.org>
To: David Howells <dhowells@...hat.com>
cc: torvalds@...l.org, akpm@...ux-foundation.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Make the kernel NTP code hand 64-bit *unsigned* values
to do_div()
Hi,
On Thu, 21 Feb 2008, David Howells wrote:
> The kernel NTP code shouldn't hand 64-bit *signed* values to do_div(). Make it
> instead hand 64-bit unsigned values. This gets rid of a couple of warnings.
I would actually prefer to introduce an explicit API for signed 64
divides to get rid of the temps completely, something like below.
Right now it uses do_div as fallback. When all archs are converted, do_div
can be single compatibility define and perhaps we can get rid of it
completely.
Bonus feature: implement the x86 version without the asm casts allowing
gcc to generate better code.
bye, Roman
---
include/asm-generic/div64.h | 14 ++++++++++++++
include/asm-i386/div64.h | 20 ++++++++++++++++++++
include/linux/calc64.h | 28 ++++++++++++++++++++++++++++
kernel/time.c | 26 +++++++-------------------
kernel/time/ntp.c | 21 +++++----------------
lib/div64.c | 21 ++++++++++++++++++++-
6 files changed, 94 insertions(+), 36 deletions(-)
Index: linux-2.6/include/asm-generic/div64.h
===================================================================
--- linux-2.6.orig/include/asm-generic/div64.h
+++ linux-2.6/include/asm-generic/div64.h
@@ -35,6 +35,20 @@ static inline uint64_t div64_64(uint64_t
return dividend / divisor;
}
+static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
+{
+ *remainder = dividend % divisor;
+ return dividend / divisor;
+}
+#define div_u64_rem div_u64_rem
+
+static inline s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
+{
+ *remainder = dividend % divisor;
+ return dividend / divisor;
+}
+#define div_s64_rem div_s64_rem
+
#elif BITS_PER_LONG == 32
extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);
Index: linux-2.6/include/asm-i386/div64.h
===================================================================
--- linux-2.6.orig/include/asm-i386/div64.h
+++ linux-2.6/include/asm-i386/div64.h
@@ -48,5 +48,25 @@ div_ll_X_l_rem(long long divs, long div,
}
+static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
+{
+ union {
+ u64 v64;
+ u32 v32[2];
+ } d = { dividend };
+ u32 upper;
+
+ upper = d.v32[1];
+ if (upper) {
+ upper = d.v32[1] % divisor;
+ d.v32[1] = d.v32[1] / divisor;
+ }
+ asm ("divl %2" : "=a" (d.v32[0]), "=d" (*remainder) :
+ "rm" (divisor), "0" (d.v32[0]), "1" (upper));
+ return d.v64;
+}
+#define div_u64_rem div_u64_rem
+
extern uint64_t div64_64(uint64_t dividend, uint64_t divisor);
+
#endif
Index: linux-2.6/include/linux/calc64.h
===================================================================
--- linux-2.6.orig/include/linux/calc64.h
+++ linux-2.6/include/linux/calc64.h
@@ -46,4 +46,32 @@ static inline long div_long_long_rem_sig
return res;
}
+#ifndef div_u64_rem
+static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
+{
+ *remainder = do_div(dividend, divisor);
+ return dividend;
+}
+#endif
+
+#ifndef div_u64
+static inline u64 div_u64(u64 dividend, u32 divisor)
+{
+ u32 remainder;
+ return div_u64_rem(dividend, divisor, &remainder);
+}
+#endif
+
+#ifndef div_s64_rem
+extern s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder);
+#endif
+
+#ifndef div_s64
+static inline s64 div_s64(s64 dividend, s32 divisor)
+{
+ s32 remainder;
+ return div_s64_rem(dividend, divisor, &remainder);
+}
+#endif
+
#endif
Index: linux-2.6/kernel/time.c
===================================================================
--- linux-2.6.orig/kernel/time.c
+++ linux-2.6/kernel/time.c
@@ -661,9 +661,7 @@ clock_t jiffies_to_clock_t(long x)
#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
return x / (HZ / USER_HZ);
#else
- u64 tmp = (u64)x * TICK_NSEC;
- do_div(tmp, (NSEC_PER_SEC / USER_HZ));
- return (long)tmp;
+ return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
#endif
}
EXPORT_SYMBOL(jiffies_to_clock_t);
@@ -675,16 +673,12 @@ unsigned long clock_t_to_jiffies(unsigne
return ~0UL;
return x * (HZ / USER_HZ);
#else
- u64 jif;
-
/* Don't worry about loss of precision here .. */
if (x >= ~0UL / HZ * USER_HZ)
return ~0UL;
/* .. but do try to contain it here */
- jif = x * (u64) HZ;
- do_div(jif, USER_HZ);
- return jif;
+ return div_u64((u64)x * HZ, USER_HZ);
#endif
}
EXPORT_SYMBOL(clock_t_to_jiffies);
@@ -692,17 +686,15 @@ EXPORT_SYMBOL(clock_t_to_jiffies);
u64 jiffies_64_to_clock_t(u64 x)
{
#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
- do_div(x, HZ / USER_HZ);
+ return div_u64(x, HZ / USER_HZ);
#else
/*
* There are better ways that don't overflow early,
* but even this doesn't overflow in hundreds of years
* in 64 bits, so..
*/
- x *= TICK_NSEC;
- do_div(x, (NSEC_PER_SEC / USER_HZ));
+ return div_u64(x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
#endif
- return x;
}
EXPORT_SYMBOL(jiffies_64_to_clock_t);
@@ -710,21 +702,17 @@ EXPORT_SYMBOL(jiffies_64_to_clock_t);
u64 nsec_to_clock_t(u64 x)
{
#if (NSEC_PER_SEC % USER_HZ) == 0
- do_div(x, (NSEC_PER_SEC / USER_HZ));
+ return div_u64(x, NSEC_PER_SEC / USER_HZ);
#elif (USER_HZ % 512) == 0
- x *= USER_HZ/512;
- do_div(x, (NSEC_PER_SEC / 512));
+ return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
#else
/*
* max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
* overflow after 64.99 years.
* exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
*/
- x *= 9;
- do_div(x, (unsigned long)((9ull * NSEC_PER_SEC + (USER_HZ/2)) /
- USER_HZ));
+ return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
#endif
- return x;
}
#if (BITS_PER_LONG < 64)
Index: linux-2.6/kernel/time/ntp.c
===================================================================
--- linux-2.6.orig/kernel/time/ntp.c
+++ linux-2.6/kernel/time/ntp.c
@@ -53,10 +53,8 @@ static void ntp_update_frequency(void)
tick_length_base = second_length;
- do_div(second_length, HZ);
- tick_nsec = second_length >> TICK_LENGTH_SHIFT;
-
- do_div(tick_length_base, NTP_INTERVAL_FREQ);
+ tick_nsec = div_u64(second_length, HZ) >> TICK_LENGTH_SHIFT;
+ tick_length_base = div_u64(tick_length_base, NTP_INTERVAL_FREQ);
}
/**
@@ -197,7 +195,7 @@ void __attribute__ ((weak)) notify_arch_
int do_adjtimex(struct timex *txc)
{
long mtemp, save_adjust, rem;
- s64 freq_adj, temp64;
+ s64 freq_adj;
int result;
/* In order to modify anything, you gotta be super-user! */
@@ -300,17 +298,8 @@ int do_adjtimex(struct timex *txc)
freq_adj = time_offset * mtemp;
freq_adj = shift_right(freq_adj, time_constant * 2 +
(SHIFT_PLL + 2) * 2 - SHIFT_NSEC);
- if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC)) {
- temp64 = time_offset << (SHIFT_NSEC - SHIFT_FLL);
- if (time_offset < 0) {
- temp64 = -temp64;
- do_div(temp64, mtemp);
- freq_adj -= temp64;
- } else {
- do_div(temp64, mtemp);
- freq_adj += temp64;
- }
- }
+ if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp > MAXSEC))
+ freq_adj += div_s64(time_offset << (SHIFT_NSEC - SHIFT_FLL), mtemp);
freq_adj += time_freq;
freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
Index: linux-2.6/lib/div64.c
===================================================================
--- linux-2.6.orig/lib/div64.c
+++ linux-2.6/lib/div64.c
@@ -18,7 +18,7 @@
#include <linux/types.h>
#include <linux/module.h>
-#include <asm/div64.h>
+#include <linux/calc64.h>
/* Not needed on 64bit architectures */
#if BITS_PER_LONG == 32
@@ -78,4 +78,23 @@ uint64_t div64_64(uint64_t dividend, uin
}
EXPORT_SYMBOL(div64_64);
+#ifndef div_s64_rem
+s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
+{
+ u64 quotient;
+
+ if (dividend < 0) {
+ quotient = div_u64_rem(-dividend, abs(divisor), (u32 *)remainder);
+ *remainder = -*remainder;
+ if (divisor > 0)
+ quotient = -quotient;
+ } else {
+ quotient = div_u64_rem(dividend, abs(divisor), (u32 *)remainder);
+ if (divisor < 0)
+ quotient = -quotient;
+ }
+ return quotient;
+}
+#endif
+
#endif /* BITS_PER_LONG == 32 */
--
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