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cleanup 64bit divide API

RFC PATCH In review [email protected] 4 participants 11 messages Mar 13, 2008 – Mar 19, 2008

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Networking Memory management x86 Library code +9 more subsystems
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[email protected]

author
#0 lore raw

cover cleanup 64bit divide API

Hi,

The primary purpose of these patches is to introduce a signed divide, which is useful for NTP. While I'm at it I cleaned up the API, so it should be a little easier to use.
It uses a new header <linux/math64.h> for it instead of using <asm-generic/div64.h>. asm-generic/div64.h has the problem of an all-or-nothing approach, so any arch not using it has to implement the whole API and usually it's enough to provide only one of them. <linux/math64.h> allows to selectively functions as needed.

In the long term we can first depricate using <asm/div64.h> and even later do_div() completely.

bye, Roman

author
#1 lore raw

[PATCH 5/4] 2.6.25-rc5-mm1 specifc div64_u64 fixes

Rename a few more div64_u64 which are only in -mm.

Signed-off-by Roman Zippel <[email protected]>
---
 arch/x86/kvm/i8254.c |    6 +++---
 kernel/time.c        |    2 +-
 2 files changed, 4 insertions(+), 4 deletions(-)
arch/x86/kvm/i8254.c +3 -3
Index: linux-2.6-mm/arch/x86/kvm/i8254.c
===================================================================
@@ -35,7 +35,7 @@
 #include "i8254.h"
 
 #ifndef CONFIG_X86_64
-#define mod_64(x, y) ((x) - (y) * div64_64(x, y))
+#define mod_64(x, y) ((x) - (y) * div64_u64(x, y))
 #else
 #define mod_64(x, y) ((x) % (y))
 #endif

@@ -60,8 +60,8 @@ static u64 muldiv64(u64 a, u32 b, u32 c)
 	rl = (u64)u.l.low * (u64)b;
 	rh = (u64)u.l.high * (u64)b;
 	rh += (rl >> 32);
-	res.l.high = div64_64(rh, c);
-	res.l.low = div64_64(((mod_64(rh, c) << 32) + (rl & 0xffffffff)), c);
+	res.l.high = div64_u64(rh, c);
+	res.l.low = div64_u64(((mod_64(rh, c) << 32) + (rl & 0xffffffff)), c);
 	return res.ll;
 }
kernel/time.c +1 -1
Index: linux-2.6-mm/kernel/time.c
===================================================================
@@ -272,7 +272,7 @@ EXPORT_SYMBOL(jiffies_to_usecs);
 
 u64 jiffies_64_to_usecs(const u64 j)
 {
-	return div64_64(j*HZ_TO_USEC_NUM + HZ_TO_USEC_DEN-1, HZ_TO_USEC_DEN);
+	return div64_u64(j*HZ_TO_USEC_NUM + HZ_TO_USEC_DEN-1, HZ_TO_USEC_DEN);
 }
 EXPORT_SYMBOL(jiffies_64_to_usecs);
author
#2 lore raw

PATCH 1/4 introduce explicit signed/unsigned 64bit divide

In reply to [email protected]

The current do_div doesn't explicitly say that it's unsigned and the signed counterpart is missing, which is e.g. needed when dealing with time values.
This introduces 64bit signed/unsigned divide functions which also attempts to cleanup the somewhat awkward calling API, which often requires the use of temporary variables for the dividend. To avoid the need for temporary variables everywhere for the remainder, each divide variant also provides a version which doesn't return the remainder.

Each architecture can now provide optimized versions of these function, otherwise generic fallback implementations will be used.

As an example I provided an alternative for the current x86 divide, which avoids the asm casts and using an union allows gcc to generate better code. It also avoids the upper divde in a few more cases, where the result is known (i.e. upper quotient is zero).

Signed-off-by Roman Zippel <[email protected]>
---
 include/asm-x86/div64.h |   20 +++++++++++++
 include/linux/math64.h  |   72 ++++++++++++++++++++++++++++++++++++++++++++++++
 lib/div64.c             |   23 ++++++++++++++-
 3 files changed, 113 insertions(+), 2 deletions(-)
include/asm-x86/div64.h +20 -0
Index: linux-2.6/include/asm-x86/div64.h
===================================================================
@@ -50,6 +50,26 @@ 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];
+	d.v32[1] = 0;
+	if (upper >= divisor) {
+		d.v32[1] = upper / divisor;
+		upper %= 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);
 
 #else
lib/div64.c +21 -2
Index: linux-2.6/lib/div64.c
===================================================================
@@ -16,9 +16,8 @@
  * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S.
  */
 
-#include <linux/types.h>
 #include <linux/module.h>
-#include <asm/div64.h>
+#include <linux/math64.h>
 
 /* Not needed on 64bit architectures */
 #if BITS_PER_LONG == 32

@@ -58,6 +57,26 @@ uint32_t __attribute__((weak)) __div64_3
 
 EXPORT_SYMBOL(__div64_32);
 
+#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;
+}
+EXPORT_SYMBOL(div_s64_rem);
+#endif
+
 /* 64bit divisor, dividend and result. dynamic precision */
 uint64_t div64_64(uint64_t dividend, uint64_t divisor)
 {
include/linux/math64.h new file +72 -0

72 lines not on this page · raw message

#3 lore raw

Re: [PATCH 1/4] introduce explicit signed/unsigned 64bit divide

Quoted 17 lines · On Thu, 13 Mar 2008, [email protected] wrote:
include/linux/math64.h new file +14 -0
@@ -0,0 +1,72 @@
+#ifndef _LINUX_MATH64_H
+#define _LINUX_MATH64_H
+
+#include <linux/types.h>
+#include <asm/div64.h>
+
+#if BITS_PER_LONG == 64
+
+/**
+ * div_u64_rem - unsigned 64bit divide with 32bit divisor with remainder
+ *
+ * This is commonly provided by 32bit archs to provide an optimized 64bit
+ * divide.
+ */

include/linux/math64.h line 24

Quoted 10 lines
include/linux/math64.h new file +10 -0
+static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
+{
+	*remainder = dividend % divisor;
+	return dividend / divisor;
+}
+
+/**
+ * div_s64_rem - signed 64bit divide with 32bit divisor with remainder
+ */
+static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)

^ ^ ^ ^ ^
s64 div_s64_rem s64 s32 s32

Quoted 8 lines
include/linux/math64.h new file +8 -0
+{
+	*remainder = dividend % divisor;
+	return dividend / divisor;
+}
+
+#elif BITS_PER_LONG == 32
+
+#ifndef div_u64_rem

include/linux/math64.h line 42

Quoted 10 lines
include/linux/math64.h new file +10 -0
+static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
+{
+	*remainder = do_div(dividend, divisor);
+	return dividend;
+}
+#endif
+
+#ifndef div_s64_rem
+extern s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder);
+#endif

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Network and Software Technology Center Europe
The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium

Phone:    +32 (0)2 700 8453
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author
#4 lore raw

Re: [PATCH 1/4] introduce explicit signed/unsigned 64bit divide

Hi,

Quoted 3 lines · Geert Uytterhoeven
Quoted 1 line

+static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)

^ ^ ^ ^ ^
s64 div_s64_rem s64 s32 s32

Thanks for noticing.
I'm quite sure I fixed this before, as I compiled this also for 64bit, so I'm not sure how it got back. Anyway, new patch below.

bye, Roman

[PATCH 1/4] introduce explicit signed/unsigned 64bit divide

The current do_div doesn't explicitly say that it's unsigned and the signed counterpart is missing, which is e.g. needed when dealing with time values.
This introduces 64bit signed/unsigned divide functions which also attempts to cleanup the somewhat awkward calling API, which often requires the use of temporary variables for the dividend. To avoid the need for temporary variables everywhere for the remainder, each divide variant also provides a version which doesn't return the remainder.

Each architecture can now provide optimized versions of these function, otherwise generic fallback implementations will be used.

As an example I provided an alternative for the current x86 divide, which avoids the asm casts and using an union allows gcc to generate better code. It also avoids the upper divde in a few more cases, where the result is known (i.e. upper quotient is zero).

Signed-off-by Roman Zippel <[email protected]>
---
 include/asm-x86/div64.h |   20 +++++++++++++
 include/linux/math64.h  |   72 ++++++++++++++++++++++++++++++++++++++++++++++++
 lib/div64.c             |   23 ++++++++++++++-
 3 files changed, 113 insertions(+), 2 deletions(-)
include/asm-x86/div64.h +20 -0
Index: linux-2.6/include/asm-x86/div64.h
===================================================================
@@ -50,6 +50,26 @@ 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];
+	d.v32[1] = 0;
+	if (upper >= divisor) {
+		d.v32[1] = upper / divisor;
+		upper %= 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);
 
 #else
lib/div64.c +21 -2
Index: linux-2.6/lib/div64.c
===================================================================
@@ -16,9 +16,8 @@
  * assembly versions such as arch/ppc/lib/div64.S and arch/sh/lib/div64.S.
  */
 
-#include <linux/types.h>
 #include <linux/module.h>
-#include <asm/div64.h>
+#include <linux/math64.h>
 
 /* Not needed on 64bit architectures */
 #if BITS_PER_LONG == 32

@@ -58,6 +57,26 @@ uint32_t __attribute__((weak)) __div64_3
 
 EXPORT_SYMBOL(__div64_32);
 
+#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;
+}
+EXPORT_SYMBOL(div_s64_rem);
+#endif
+
 /* 64bit divisor, dividend and result. dynamic precision */
 uint64_t div64_64(uint64_t dividend, uint64_t divisor)
 {
include/linux/math64.h new file +72 -0

72 lines not on this page · raw message

maintainer
#5 lore raw

Re: [PATCH 1/4] introduce explicit signed/unsigned 64bit divide

Quoted 9 lines · On Thu, 13 Mar 2008 15:59:27 +0100 (CET) Roman Zippel <[email protected]>…
Quoted 3 lines · Geert Uytterhoeven
Quoted 1 line

+static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)

^ ^ ^ ^ ^
s64 div_s64_rem s64 s32 s32

Thanks for noticing.
I'm quite sure I fixed this before, as I compiled this also for 64bit, so I'm not sure how it got back. Anyway, new patch below.

I think what happened was that [patch 3/4] fixed this up. Of course, that patch doesn't apply on this updated [1/4]. I _could_ just take the old [1/4] (I think), but I don't know if that wouild be bisection-friendly.

Anyway, please redo&resend? Thanks.

Please have a think about that code in arch/x86/kvm/i8254.c too. It is painful to see remote subsystems (re)implementing generic infrastructure. Can KVM use existing code? Should we hoist what KVM has done there into generic code? Did it have to use a(nother bleeding) macro?

author
#6 lore raw

Re: [PATCH 1/4] introduce explicit signed/unsigned 64bit divide

Hi,

Quoted 5 lines · Andrew Morton

I think what happened was that [patch 3/4] fixed this up. Of course, that patch doesn't apply on this updated [1/4]. I _could_ just take the old [1/4] (I think), but I don't know if that wouild be bisection-friendly.

Anyway, please redo&resend? Thanks.

Done.

Quoted 4 lines

Please have a think about that code in arch/x86/kvm/i8254.c too. It is painful to see remote subsystems (re)implementing generic infrastructure. Can KVM use existing code? Should we hoist what KVM has done there into generic code? Did it have to use a(nother bleeding) macro?

Looker closer at it, div64_u64() seems to be a bit overkill, as the divisor is a 32bit value, so the following should do the same job (only compile tested):

u64 muldiv64(u64 a, u32 b, u32 c)

{       
	union { 
		u64 ll;
		struct {
			u32 low, high;
		};
	} u, res, rl, rh;

	u.ll = a;
	rl.ll = (u64)b * u.low;
	rh.ll = (u64)b * u.high;
	rh.ll += rl.high;
	res.high = div_u64_rem(rh.ll, c, &rl.high);
	res.low = div_u64(rl.ll, c);
	return res.ll;
}

Moving it to a more generic location shouldn't be a big problem.

bye, Roman

author
#7 lore raw

PATCH 2/4 convert a few do_div user

In reply to [email protected]

This converts a few users of do_div to div_[su]64 and this demonstrates nicely how it can reduce some expressions to one-liners.

Signed-off-by Roman Zippel <[email protected]>
---
 kernel/time.c     |   29 +++++++++--------------------
 kernel/time/ntp.c |   25 ++++++-------------------
 2 files changed, 15 insertions(+), 39 deletions(-)
kernel/time.c +9 -20
Index: linux-2.6/kernel/time.c
===================================================================
@@ -35,6 +35,7 @@
 #include <linux/syscalls.h>
 #include <linux/security.h>
 #include <linux/fs.h>
+#include <linux/math64.h>
 
 #include <asm/uaccess.h>
 #include <asm/unistd.h>

@@ -585,9 +586,7 @@ clock_t jiffies_to_clock_t(long x)
 	return x / (HZ / USER_HZ);
 # endif
 #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);

@@ -599,16 +598,12 @@ 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);

@@ -617,10 +612,9 @@ u64 jiffies_64_to_clock_t(u64 x)
 {
 #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
 # if HZ < USER_HZ
-	x *= USER_HZ;
-	do_div(x, HZ);
+	x = div_u64(x * USER_HZ, HZ);
 # elif HZ > USER_HZ
-	do_div(x, HZ / USER_HZ);
+	x = div_u64(x, HZ / USER_HZ);
 # else
 	/* Nothing to do */
 # endif

@@ -630,8 +624,7 @@ u64 jiffies_64_to_clock_t(u64 x)
 	 * 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));
+	x = div_u64(x * TICK_NSEC, (NSEC_PER_SEC / USER_HZ));
 #endif
 	return x;
 }

@@ -640,21 +633,17 @@ 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)
kernel/time/ntp.c +6 -19
Index: linux-2.6/kernel/time/ntp.c
===================================================================
@@ -15,7 +15,7 @@
 #include <linux/jiffies.h>
 #include <linux/hrtimer.h>
 #include <linux/capability.h>
-#include <asm/div64.h>
+#include <linux/math64.h>
 #include <asm/timex.h>
 
 /*

@@ -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);
 }
 
 /**

@@ -237,7 +235,7 @@ static inline void notify_cmos_timer(voi
 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! */

@@ -342,19 +340,8 @@ 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)) {
-			u64 utemp64;
-			temp64 = time_offset << (SHIFT_NSEC - SHIFT_FLL);
-			if (time_offset < 0) {
-			    utemp64 = -temp64;
-			    do_div(utemp64, mtemp);
-			    freq_adj -= utemp64;
-			} else {
-			    utemp64 = temp64;
-			    do_div(utemp64, mtemp);
-			    freq_adj += utemp64;
-			}
-		    }
+		    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);
#8 lore raw

Re: [PATCH 2/4] convert a few do_div user

Quoted 10 lines · [email protected] wrote:

This converts a few users of do_div to div_[su]64 and this demonstrates nicely how it can reduce some expressions to one-liners.

Signed-off-by Roman Zippel <[email protected]>
---
 kernel/time.c     |   29 +++++++++--------------------
 kernel/time/ntp.c |   25 ++++++-------------------
 2 files changed, 15 insertions(+), 39 deletions(-)

<snip>

Quoted 4 lines

Index: linux-2.6/kernel/time/ntp.c
===================================================================

kernel/time/ntp.c +0 -0

<snip>

kernel/time/ntp.c static void ntp_update_frequency(void) · line 59

Quoted 13 lines

/*

kernel/time/ntp.c +2 -4
@@ -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);
 }

Probably the compiler would optimize it, but maybe its clearer to change it this way:

- 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(second_length, NTP_INTERVAL_FREQ);

Signature · 6 lines
Regards,
Jörg-Volker.



<snip>
author
#9 lore raw

PATCH 3/4 rename div64_64 to div64_u64

In reply to [email protected]

Rename div64_64 to div64_u64 to make it consistent with the other divide functions, so it clearly includes the type of the divide. Move its definition to math64.h as currently no architecture overrides the generic implementation. They can still override it of course, but the duplicated declarations are avoided.

Signed-off-by Roman Zippel <[email protected]>
---
 arch/x86/kvm/lapic.c         |    6 +++---
 include/asm-arm/div64.h      |    2 --
 include/asm-generic/div64.h  |    7 -------
 include/asm-m68k/div64.h     |    1 -
 include/asm-mips/div64.h     |    6 ------
 include/asm-mn10300/div64.h  |    3 ---
 include/asm-um/div64.h       |    1 -
 include/asm-x86/div64.h      |    2 --
 include/linux/math64.h       |   14 +++++++++++++-
 kernel/sched.c               |    7 ++++---
 kernel/sched_debug.c         |    4 ++--
 lib/div64.c                  |   12 ++++++------
 net/ipv4/tcp_cubic.c         |    4 ++--
 net/netfilter/xt_connbytes.c |    5 ++---
 14 files changed, 32 insertions(+), 42 deletions(-)
arch/x86/kvm/lapic.c +3 -3
Index: linux-2.6/arch/x86/kvm/lapic.c
===================================================================
@@ -25,13 +25,13 @@
 #include <linux/hrtimer.h>
 #include <linux/io.h>
 #include <linux/module.h>
+#include <linux/math64.h>
 #include <asm/processor.h>
 #include <asm/msr.h>
 #include <asm/page.h>
 #include <asm/current.h>
 #include <asm/apicdef.h>
 #include <asm/atomic.h>
-#include <asm/div64.h>
 #include "irq.h"
 
 #define PRId64 "d"

@@ -526,8 +526,8 @@ static u32 apic_get_tmcct(struct kvm_lap
 	} else
 		passed = ktime_sub(now, apic->timer.last_update);
 
-	counter_passed = div64_64(ktime_to_ns(passed),
-				  (APIC_BUS_CYCLE_NS * apic->timer.divide_count));
+	counter_passed = div64_u64(ktime_to_ns(passed),
+				   (APIC_BUS_CYCLE_NS * apic->timer.divide_count));
 
 	if (counter_passed > tmcct) {
 		if (unlikely(!apic_lvtt_period(apic))) {
include/asm-arm/div64.h +0 -2
Index: linux-2.6/include/asm-arm/div64.h
===================================================================
@@ -224,6 +224,4 @@
 
 #endif
 
-extern uint64_t div64_64(uint64_t dividend, uint64_t divisor);
-
 #endif
include/asm-generic/div64.h +0 -7
Index: linux-2.6/include/asm-generic/div64.h
===================================================================
@@ -30,11 +30,6 @@
 	__rem;							\
  })
 
-static inline uint64_t div64_64(uint64_t dividend, uint64_t divisor)
-{
-	return dividend / divisor;
-}
-
 #elif BITS_PER_LONG == 32
 
 extern uint32_t __div64_32(uint64_t *dividend, uint32_t divisor);

@@ -54,8 +49,6 @@ extern uint32_t __div64_32(uint64_t *div
 	__rem;						\
  })
 
-extern uint64_t div64_64(uint64_t dividend, uint64_t divisor);
-
 #else /* BITS_PER_LONG == ?? */
 
 # error do_div() does not yet support the C64
include/asm-m68k/div64.h +0 -1
Index: linux-2.6/include/asm-m68k/div64.h
===================================================================
@@ -25,5 +25,4 @@
 	__rem;							\
 })
 
-extern uint64_t div64_64(uint64_t dividend, uint64_t divisor);
 #endif /* _M68K_DIV64_H */
include/asm-mips/div64.h +0 -6
Index: linux-2.6/include/asm-mips/div64.h
===================================================================
@@ -82,7 +82,6 @@
 	(n) = __quot; \
 	__mod; })
 
-extern uint64_t div64_64(uint64_t dividend, uint64_t divisor);
 #endif /* (_MIPS_SZLONG == 32) */
 
 #if (_MIPS_SZLONG == 64)

@@ -106,11 +105,6 @@ extern uint64_t div64_64(uint64_t divide
 	(n) = __quot; \
 	__mod; })
 
-static inline uint64_t div64_64(uint64_t dividend, uint64_t divisor)
-{
-	return dividend / divisor;
-}
-
 #endif /* (_MIPS_SZLONG == 64) */
 
 #endif /* _ASM_DIV64_H */
include/asm-mn10300/div64.h +0 -3
Index: linux-2.6/include/asm-mn10300/div64.h
===================================================================
@@ -97,7 +97,4 @@ signed __muldiv64s(signed val, signed mu
 	return result;
 }
 
-extern __attribute__((const))
-uint64_t div64_64(uint64_t dividend, uint64_t divisor);
-
 #endif /* _ASM_DIV64 */
include/asm-um/div64.h +0 -1
Index: linux-2.6/include/asm-um/div64.h
===================================================================
@@ -3,5 +3,4 @@
 
 #include "asm/arch/div64.h"
 
-extern uint64_t div64_64(uint64_t dividend, uint64_t divisor);
 #endif
include/asm-x86/div64.h +0 -2
Index: linux-2.6/include/asm-x86/div64.h
===================================================================
@@ -70,8 +70,6 @@ static inline u64 div_u64_rem(u64 divide
 }
 #define div_u64_rem	div_u64_rem
 
-extern uint64_t div64_64(uint64_t dividend, uint64_t divisor);
-
 #else
 # include <asm-generic/div64.h>
 #endif /* CONFIG_X86_32 */
include/linux/math64.h +13 -1
Index: linux-2.6/include/linux/math64.h
===================================================================
@@ -21,12 +21,20 @@ static inline u64 div_u64_rem(u64 divide
 /**
  * div_s64_rem - signed 64bit divide with 32bit divisor with remainder
  */
-static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
+static inline s64 div_s64_rem(s64 dividend, s32 divisor, s32 *remainder)
 {
 	*remainder = dividend % divisor;
 	return dividend / divisor;
 }
 
+/**
+ * div64_u64 - unsigned 64bit divide with 64bit divisor
+ */
+static inline u64 div64_u64(u64 dividend, u64 divisor)
+{
+	return dividend / divisor;
+}
+
 #elif BITS_PER_LONG == 32
 
 #ifndef div_u64_rem

@@ -69,4 +77,8 @@ static inline s64 div_s64(s64 dividend, 
 }
 #endif
 
+#ifndef div64_u64
+extern u64 div64_u64(u64 dividend, u64 divisor);
+#endif
+
 #endif /* _LINUX_MATH64_H */
kernel/sched.c +3 -3
Index: linux-2.6/kernel/sched.c
===================================================================
@@ -7112,7 +7113,7 @@ static void init_tg_cfs_entry(struct rq 
 	se->cfs_rq = &rq->cfs;
 	se->my_q = cfs_rq;
 	se->load.weight = tg->shares;
-	se->load.inv_weight = div64_64(1ULL<<32, se->load.weight);
+	se->load.inv_weight = div64_u64(1ULL<<32, se->load.weight);
 	se->parent = NULL;
 }
 #endif

@@ -7649,7 +7650,7 @@ static void set_se_shares(struct sched_e
 		dequeue_entity(cfs_rq, se, 0);
 
 	se->load.weight = shares;
-	se->load.inv_weight = div64_64((1ULL<<32), shares);
+	se->load.inv_weight = div64_u64((1ULL<<32), shares);
 
 	if (on_rq)
 		enqueue_entity(cfs_rq, se, 0);

@@ -7722,7 +7723,7 @@ static unsigned long to_ratio(u64 period
 	if (runtime == RUNTIME_INF)
 		return 1ULL << 16;
 
-	return div64_64(runtime << 16, period);
+	return div64_u64(runtime << 16, period);
 }
 
 static int __rt_schedulable(struct task_group *tg, u64 period, u64 runtime)
kernel/sched_debug.c +2 -2
Index: linux-2.6/kernel/sched_debug.c
===================================================================
@@ -331,8 +331,8 @@ void proc_sched_show_task(struct task_st
 
 		avg_per_cpu = p->se.sum_exec_runtime;
 		if (p->se.nr_migrations) {
-			avg_per_cpu = div64_64(avg_per_cpu,
-					       p->se.nr_migrations);
+			avg_per_cpu = div64_u64(avg_per_cpu,
+						p->se.nr_migrations);
 		} else {
 			avg_per_cpu = -1LL;
 		}
lib/div64.c +6 -6
Index: linux-2.6/lib/div64.c
===================================================================
@@ -78,9 +78,10 @@ EXPORT_SYMBOL(div_s64_rem);
 #endif
 
 /* 64bit divisor, dividend and result. dynamic precision */
-uint64_t div64_64(uint64_t dividend, uint64_t divisor)
+#ifndef div64_u64
+u64 div64_u64(u64 dividend, u64 divisor)
 {
-	uint32_t high, d;
+	u32 high, d;
 
 	high = divisor >> 32;
 	if (high) {

@@ -91,10 +92,9 @@ uint64_t div64_64(uint64_t dividend, uin
 	} else
 		d = divisor;
 
-	do_div(dividend, d);
-
-	return dividend;
+	return div_u64(dividend, d);
 }
-EXPORT_SYMBOL(div64_64);
+EXPORT_SYMBOL(div64_u64);
+#endif
 
 #endif /* BITS_PER_LONG == 32 */
net/ipv4/tcp_cubic.c +2 -2
Index: linux-2.6/net/ipv4/tcp_cubic.c
===================================================================
@@ -14,8 +14,8 @@
 
 #include <linux/mm.h>
 #include <linux/module.h>
+#include <linux/math64.h>
 #include <net/tcp.h>
-#include <asm/div64.h>
 
 #define BICTCP_BETA_SCALE    1024	/* Scale factor beta calculation
 					 * max_cwnd = snd_cwnd * beta

@@ -134,7 +134,7 @@ static u32 cubic_root(u64 a)
 	 * x    = ( 2 * x  +  a / x  ) / 3
 	 *  k+1          k         k
 	 */
-	x = (2 * x + (u32)div64_64(a, (u64)x * (u64)(x - 1)));
+	x = (2 * x + (u32)div64_u64(a, (u64)x * (u64)(x - 1)));
 	x = ((x * 341) >> 10);
 	return x;
 }
net/netfilter/xt_connbytes.c +2 -3
Index: linux-2.6/net/netfilter/xt_connbytes.c
===================================================================
@@ -4,12 +4,11 @@
 #include <linux/module.h>
 #include <linux/bitops.h>
 #include <linux/skbuff.h>
+#include <linux/math64.h>
 #include <linux/netfilter/x_tables.h>
 #include <linux/netfilter/xt_connbytes.h>
 #include <net/netfilter/nf_conntrack.h>
 
-#include <asm/div64.h>
-
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("Harald Welte <[email protected]>");
 MODULE_DESCRIPTION("Xtables: Number of packets/bytes per connection matching");

@@ -82,7 +81,7 @@ connbytes_mt(const struct sk_buff *skb, 
 			break;
 		}
 		if (pkts != 0)
-			what = div64_64(bytes, pkts);
+			what = div64_u64(bytes, pkts);
 		break;
 	}
author
#10 lore raw

PATCH 4/4 remove div_long_long_rem

In reply to [email protected]

x86 is the only arch right now, which provides an optimized for div_long_long_rem and it has the downside that one has to be very careful that the divide doesn't overflow.
The API is a little akward, as the arguments for the unsigned divide are signed. The signed version also doesn't handle a negative divisor and produces worse code on 64bit archs.
There is little incentive to keep this API alive, so this converts the few users to the new API.

Signed-off-by Roman Zippel <[email protected]>
---
 arch/mips/kernel/binfmt_elfn32.c |    5 ++-
 arch/mips/kernel/binfmt_elfo32.c |    5 ++-
 drivers/char/mmtimer.c           |   24 ++++++++-----------
 include/asm-x86/div64.h          |   19 ---------------
 include/linux/calc64.h           |   49 ---------------------------------------
 include/linux/jiffies.h          |    2 -
 kernel/posix-cpu-timers.c        |   11 +++-----
 kernel/time.c                    |   25 +++++++++++--------
 kernel/time/ntp.c                |    6 +---
 mm/slub.c                        |    9 +++----
 10 files changed, 44 insertions(+), 111 deletions(-)
arch/mips/kernel/binfmt_elfn32.c +3 -2
Index: linux-2.6/arch/mips/kernel/binfmt_elfn32.c
===================================================================
@@ -54,6 +54,7 @@ typedef elf_fpreg_t elf_fpregset_t[ELF_N
 #include <linux/module.h>
 #include <linux/elfcore.h>
 #include <linux/compat.h>
+#include <linux/math64.h>
 
 #define elf_prstatus elf_prstatus32
 struct elf_prstatus32

@@ -102,8 +103,8 @@ jiffies_to_compat_timeval(unsigned long 
 	 * one divide.
 	 */
 	u64 nsec = (u64)jiffies * TICK_NSEC;
-	long rem;
-	value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &rem);
+	u32 rem;
+	value->tv_sec = div_u64_rem(nsec, NSEC_PER_SEC, &rem);
 	value->tv_usec = rem / NSEC_PER_USEC;
 }
arch/mips/kernel/binfmt_elfo32.c +3 -2
Index: linux-2.6/arch/mips/kernel/binfmt_elfo32.c
===================================================================
@@ -56,6 +56,7 @@ typedef elf_fpreg_t elf_fpregset_t[ELF_N
 #include <linux/module.h>
 #include <linux/elfcore.h>
 #include <linux/compat.h>
+#include <linux/math64.h>
 
 #define elf_prstatus elf_prstatus32
 struct elf_prstatus32

@@ -104,8 +105,8 @@ jiffies_to_compat_timeval(unsigned long 
 	 * one divide.
 	 */
 	u64 nsec = (u64)jiffies * TICK_NSEC;
-	long rem;
-	value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &rem);
+	u32 rem;
+	value->tv_sec = div_u64_rem(nsec, NSEC_PER_SEC, &rem);
 	value->tv_usec = rem / NSEC_PER_USEC;
 }
drivers/char/mmtimer.c +11 -13
Index: linux-2.6/drivers/char/mmtimer.c
===================================================================
@@ -30,6 +30,8 @@
 #include <linux/miscdevice.h>
 #include <linux/posix-timers.h>
 #include <linux/interrupt.h>
+#include <linux/time.h>
+#include <linux/math64.h>
 
 #include <asm/uaccess.h>
 #include <asm/sn/addrs.h>

@@ -366,8 +368,8 @@ static int sgi_clock_get(clockid_t clock
 
 	nsec = rtc_time() * sgi_clock_period
 			+ sgi_clock_offset.tv_nsec;
-	tp->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &tp->tv_nsec)
-			+ sgi_clock_offset.tv_sec;
+	*tp = ns_to_timespec(nsec);
+	tp->tv_sec += sgi_clock_offset.tv_sec;
 	return 0;
 };
 

@@ -375,11 +377,11 @@ static int sgi_clock_set(clockid_t clock
 {
 
 	u64 nsec;
-	u64 rem;
+	u32 rem;
 
 	nsec = rtc_time() * sgi_clock_period;
 
-	sgi_clock_offset.tv_sec = tp->tv_sec - div_long_long_rem(nsec, NSEC_PER_SEC, &rem);
+	sgi_clock_offset.tv_sec = tp->tv_sec - div_u64_rem(nsec, NSEC_PER_SEC, &rem);
 
 	if (rem <= tp->tv_nsec)
 		sgi_clock_offset.tv_nsec = tp->tv_sec - rem;

@@ -532,9 +534,6 @@ static int sgi_timer_del(struct k_itimer
 	return 0;
 }
 
-#define timespec_to_ns(x) ((x).tv_nsec + (x).tv_sec * NSEC_PER_SEC)
-#define ns_to_timespec(ts, nsec) (ts).tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &(ts).tv_nsec)
-
 /* Assumption: it_lock is already held with irq's disabled */
 static void sgi_timer_get(struct k_itimer *timr, struct itimerspec *cur_setting)
 {

@@ -547,9 +546,8 @@ static void sgi_timer_get(struct k_itime
 		return;
 	}
 
-	ns_to_timespec(cur_setting->it_interval, timr->it.mmtimer.incr * sgi_clock_period);
-	ns_to_timespec(cur_setting->it_value, (timr->it.mmtimer.expires - rtc_time())* sgi_clock_period);
-	return;
+	cur_setting->it_interval = ns_to_timespec(timr->it.mmtimer.incr * sgi_clock_period);
+	cur_setting->it_value = ns_to_timespec((timr->it.mmtimer.expires - rtc_time()) * sgi_clock_period);
 }
 
 

@@ -568,8 +566,8 @@ static int sgi_timer_set(struct k_itimer
 		sgi_timer_get(timr, old_setting);
 
 	sgi_timer_del(timr);
-	when = timespec_to_ns(new_setting->it_value);
-	period = timespec_to_ns(new_setting->it_interval);
+	when = timespec_to_ns(&new_setting->it_value);
+	period = timespec_to_ns(&new_setting->it_interval);
 
 	if (when == 0)
 		/* Clear timer */

@@ -580,7 +578,7 @@ static int sgi_timer_set(struct k_itimer
 		unsigned long now;
 
 		getnstimeofday(&n);
-		now = timespec_to_ns(n);
+		now = timespec_to_ns(&n);
 		if (when > now)
 			when -= now;
 		else
include/asm-x86/div64.h +0 -19
Index: linux-2.6/include/asm-x86/div64.h
===================================================================
@@ -31,25 +31,6 @@
 	__mod; \
 })
 
-/*
- * (long)X = ((long long)divs) / (long)div
- * (long)rem = ((long long)divs) % (long)div
- *
- * Warning, this will do an exception if X overflows.
- */
-#define div_long_long_rem(a,b,c) div_ll_X_l_rem(a,b,c)
-
-static inline long
-div_ll_X_l_rem(long long divs, long div, long *rem)
-{
-	long dum2;
-      __asm__("divl %2":"=a"(dum2), "=d"(*rem)
-      :	"rm"(div), "A"(divs));
-
-	return dum2;
-
-}
-
 static inline u64 div_u64_rem(u64 dividend, u32 divisor, u32 *remainder)
 {
 	union {
include/linux/calc64.h deleted +0 -49

49 lines not on this page · raw message

include/linux/jiffies.h +1 -1
Index: linux-2.6/include/linux/jiffies.h
===================================================================
@@ -1,7 +1,7 @@
 #ifndef _LINUX_JIFFIES_H
 #define _LINUX_JIFFIES_H
 
-#include <linux/calc64.h>
+#include <linux/math64.h>
 #include <linux/kernel.h>
 #include <linux/types.h>
 #include <linux/time.h>
kernel/posix-cpu-timers.c +5 -6
Index: linux-2.6/kernel/posix-cpu-timers.c
===================================================================
@@ -4,8 +4,9 @@
 
 #include <linux/sched.h>
 #include <linux/posix-timers.h>
-#include <asm/uaccess.h>
 #include <linux/errno.h>
+#include <linux/math64.h>
+#include <asm/uaccess.h>
 
 static int check_clock(const clockid_t which_clock)
 {

@@ -47,12 +48,10 @@ static void sample_to_timespec(const clo
 			       union cpu_time_count cpu,
 			       struct timespec *tp)
 {
-	if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED) {
-		tp->tv_sec = div_long_long_rem(cpu.sched,
-					       NSEC_PER_SEC, &tp->tv_nsec);
-	} else {
+	if (CPUCLOCK_WHICH(which_clock) == CPUCLOCK_SCHED)
+		*tp = ns_to_timespec(cpu.sched);
+	else
 		cputime_to_timespec(cpu.cpu, tp);
-	}
 }
 
 static inline int cpu_time_before(const clockid_t which_clock,
kernel/time.c +15 -10
Index: linux-2.6/kernel/time.c
===================================================================
@@ -390,13 +390,17 @@ void set_normalized_timespec(struct time
 struct timespec ns_to_timespec(const s64 nsec)
 {
 	struct timespec ts;
+	s32 rem;
 
 	if (!nsec)
 		return (struct timespec) {0, 0};
 
-	ts.tv_sec = div_long_long_rem_signed(nsec, NSEC_PER_SEC, &ts.tv_nsec);
-	if (unlikely(nsec < 0))
-		set_normalized_timespec(&ts, ts.tv_sec, ts.tv_nsec);
+	ts.tv_sec = div_s64_rem(nsec, NSEC_PER_SEC, &rem);
+	if (unlikely(rem < 0)) {
+		ts.tv_sec--;
+		rem += NSEC_PER_SEC;
+	}
+	ts.tv_nsec = rem;
 
 	return ts;
 }

@@ -526,8 +530,10 @@ jiffies_to_timespec(const unsigned long 
 	 * Convert jiffies to nanoseconds and separate with
 	 * one divide.
 	 */
-	u64 nsec = (u64)jiffies * TICK_NSEC;
-	value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &value->tv_nsec);
+	u32 rem;
+	value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
+				    NSEC_PER_SEC, &rem);
+	value->tv_nsec = rem;
 }
 EXPORT_SYMBOL(jiffies_to_timespec);
 

@@ -565,12 +571,11 @@ void jiffies_to_timeval(const unsigned l
 	 * Convert jiffies to nanoseconds and separate with
 	 * one divide.
 	 */
-	u64 nsec = (u64)jiffies * TICK_NSEC;
-	long tv_usec;
+	u32 rem;
 
-	value->tv_sec = div_long_long_rem(nsec, NSEC_PER_SEC, &tv_usec);
-	tv_usec /= NSEC_PER_USEC;
-	value->tv_usec = tv_usec;
+	value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
+				    NSEC_PER_SEC, &rem);
+	value->tv_usec = rem / NSEC_PER_USEC;
 }
 EXPORT_SYMBOL(jiffies_to_timeval);
kernel/time/ntp.c +2 -4
Index: linux-2.6/kernel/time/ntp.c
===================================================================
@@ -234,7 +234,7 @@ static inline void notify_cmos_timer(voi
  */
 int do_adjtimex(struct timex *txc)
 {
-	long mtemp, save_adjust, rem;
+	long mtemp, save_adjust;
 	s64 freq_adj;
 	int result;
 

@@ -345,9 +345,7 @@ int do_adjtimex(struct timex *txc)
 		    freq_adj += time_freq;
 		    freq_adj = min(freq_adj, (s64)MAXFREQ_NSEC);
 		    time_freq = max(freq_adj, (s64)-MAXFREQ_NSEC);
-		    time_offset = div_long_long_rem_signed(time_offset,
-							   NTP_INTERVAL_FREQ,
-							   &rem);
+		    time_offset = div_s64(time_offset, NTP_INTERVAL_FREQ);
 		    time_offset <<= SHIFT_UPDATE;
 		} /* STA_PLL */
 	    } /* txc->modes & ADJ_OFFSET */
mm/slub.c +4 -5
Index: linux-2.6/mm/slub.c
===================================================================
@@ -21,6 +21,7 @@
 #include <linux/ctype.h>
 #include <linux/kallsyms.h>
 #include <linux/memory.h>
+#include <linux/math64.h>
 
 /*
  * Lock order:

@@ -3515,12 +3516,10 @@ static int list_locations(struct kmem_ca
 			len += sprintf(buf + len, "<not-available>");
 
 		if (l->sum_time != l->min_time) {
-			unsigned long remainder;
-
 			len += sprintf(buf + len, " age=%ld/%ld/%ld",
-			l->min_time,
-			div_long_long_rem(l->sum_time, l->count, &remainder),
-			l->max_time);
+				l->min_time,
+				(long)div_u64(l->sum_time, l->count),
+				l->max_time);
 		} else
 			len += sprintf(buf + len, " age=%ld",
 				l->min_time);