[PATCH] x86: tsc: get rid of custom DIV_ROUND

[PATCH] x86: tsc: get rid of custom DIV_ROUND

[Michal Nazarewicz]

When invoced for positive values, DIV_ROUND macro defined in
arch/x86/kernel/tsc.c behaves exactly like DIV_ROUND_CLOSEST from
include/linux/kernel.h file, so remove the custom macro in favour
of the shared one.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
---
 arch/x86/kernel/tsc.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

 No changes after compilation:

 $ ll tsc.o.*
 -rw------- 1 mpn eng 46497 Jun 19 03:54 tsc.o.after
 -rw------- 1 mpn eng 46497 Jun 19 03:55 tsc.o.before
 $ objdump -d tsc.o.before >tsc.s.before
 $ objdump -d tsc.o.after >tsc.s.after
 $ diff -u tsc.s.before tsc.s.after
 --- tsc.s.before	2014-06-19 03:56:54.880545041 +0200
 +++ tsc.s.after	2014-06-19 03:56:54.884545079 +0200
 @@ -1,5 +1,5 @@
  
 -tsc.o.before:     file format elf64-x86-64
 +tsc.o.after:     file format elf64-x86-64
  
  
  Disassembly of section .text:
 $

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 57e5ce1..02f21c0 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -234,9 +234,6 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
 	return ns;
 }
 
-/* XXX surely we already have this someplace in the kernel?! */
-#define DIV_ROUND(n, d) (((n) + ((d) / 2)) / (d))
-
 static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
 {
 	unsigned long long tsc_now, ns_now;
@@ -259,7 +256,8 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
 	 * time function is continuous; see the comment near struct
 	 * cyc2ns_data.
 	 */
-	data->cyc2ns_mul = DIV_ROUND(NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR, cpu_khz);
+	data->cyc2ns_mul = DIV_ROUND_CLOSEST(
+		NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR, cpu_khz);
 	data->cyc2ns_shift = CYC2NS_SCALE_FACTOR;
 	data->cyc2ns_offset = ns_now -
 		mul_u64_u32_shr(tsc_now, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);
-- 
2.0.0.526.g5318336

Re: [PATCH] x86: tsc: get rid of custom DIV_ROUND

[David Rientjes]

On Thu, 19 Jun 2014, Michal Nazarewicz wrote:

> When invoced for positive values, DIV_ROUND macro defined in
> arch/x86/kernel/tsc.c behaves exactly like DIV_ROUND_CLOSEST from
> include/linux/kernel.h file, so remove the custom macro in favour
> of the shared one.
> 
> Signed-off-by: Michal Nazarewicz <mina86@mina86.com>

Acked-by: David Rientjes <rientjes@google.com>

[tip:x86/cleanups] x86/tsc: Get rid of custom DIV_ROUND() macro

[tip-bot for Michal Nazarewicz]

Commit-ID:  891715793f0451e5114d200be932ac14ce8521a3
Gitweb:     http://git.kernel.org/tip/891715793f0451e5114d200be932ac14ce8521a3
Author:     Michal Nazarewicz <mina86@mina86.com>
AuthorDate: Thu, 19 Jun 2014 03:58:36 +0200
Committer:  H. Peter Anvin <hpa@zytor.com>
CommitDate: Thu, 19 Jun 2014 22:04:50 -0700

x86/tsc: Get rid of custom DIV_ROUND() macro

When invoced for positive values, DIV_ROUND macro defined in
arch/x86/kernel/tsc.c behaves exactly like DIV_ROUND_CLOSEST from
include/linux/kernel.h file, so remove the custom macro in favour
of the shared one.

[ hpa: changed line breaks ]

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Link: http://lkml.kernel.org/r/1403143116-21755-1-git-send-email-mina86@mina86.com
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: H. Peter Anvin <hpa@zytor.com>
---
 arch/x86/kernel/tsc.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 57e5ce1..8764232 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -234,9 +234,6 @@ static inline unsigned long long cycles_2_ns(unsigned long long cyc)
 	return ns;
 }
 
-/* XXX surely we already have this someplace in the kernel?! */
-#define DIV_ROUND(n, d) (((n) + ((d) / 2)) / (d))
-
 static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
 {
 	unsigned long long tsc_now, ns_now;
@@ -259,7 +256,9 @@ static void set_cyc2ns_scale(unsigned long cpu_khz, int cpu)
 	 * time function is continuous; see the comment near struct
 	 * cyc2ns_data.
 	 */
-	data->cyc2ns_mul = DIV_ROUND(NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR, cpu_khz);
+	data->cyc2ns_mul =
+		DIV_ROUND_CLOSEST(NSEC_PER_MSEC << CYC2NS_SCALE_FACTOR,
+				  cpu_khz);
 	data->cyc2ns_shift = CYC2NS_SCALE_FACTOR;
 	data->cyc2ns_offset = ns_now -
 		mul_u64_u32_shr(tsc_now, data->cyc2ns_mul, CYC2NS_SCALE_FACTOR);

Re: [PATCH] x86: tsc: get rid of custom DIV_ROUND

[Peter Zijlstra]

On Thu, Jun 19, 2014 at 03:58:36AM +0200, Michal Nazarewicz wrote:
> When invoced for positive values, DIV_ROUND macro defined in
> arch/x86/kernel/tsc.c behaves exactly like DIV_ROUND_CLOSEST from
> include/linux/kernel.h file, so remove the custom macro in favour
> of the shared one.

See, I knew we'd had one. _CLOSEST is a dumb postfix though, its the
default whenever people talk of rounding.

> Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
> ---
>  arch/x86/kernel/tsc.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
> 
>  No changes after compilation:
> 
>  $ ll tsc.o.*
>  -rw------- 1 mpn eng 46497 Jun 19 03:54 tsc.o.after
>  -rw------- 1 mpn eng 46497 Jun 19 03:55 tsc.o.before
>  $ objdump -d tsc.o.before >tsc.s.before
>  $ objdump -d tsc.o.after >tsc.s.after
>  $ diff -u tsc.s.before tsc.s.after
>  --- tsc.s.before	2014-06-19 03:56:54.880545041 +0200
>  +++ tsc.s.after	2014-06-19 03:56:54.884545079 +0200
>  @@ -1,5 +1,5 @@
>   
>  -tsc.o.before:     file format elf64-x86-64
>  +tsc.o.after:     file format elf64-x86-64
>   
>   
>   Disassembly of section .text:
>  $

This diff in a diff totally confused patch.

Applies when I remove that.