[PATCH] powerpc: fix wrong divisor in usecs_to_cputime

Commit d57af9b (taskstats: use real microsecond granularity for CPU times)
renamed msecs_to_cputime to usecs_to_cputime, but failed to update all
numbers on the way.  This causes nonsensical cpu idle/iowait values to be
displayed in /proc/stat (the only user of usecs_to_cputime so far).

This also renames __cputime_msec_factor to __cputime_usec_factor, adapting
its value and using it directly in cputime_to_usecs instead of doing two
multiplications.

Signed-off-by: Andreas Schwab <redacted>
---
 arch/powerpc/include/asm/cputime.h |    6 +++---
 arch/powerpc/kernel/time.c         |   10 +++++-----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/arch/powerpc/include/asm/cputime.h b/arch/powerpc/include/asm/cputime.h
index 1cf20bd..33a3580 100644
--- a/arch/powerpc/include/asm/cputime.h
+++ b/arch/powerpc/include/asm/cputime.h

@@ -126,11 +126,11 @@ static inline u64 cputime64_to_jiffies64(const cputime_t ct)
 /*
  * Convert cputime <-> microseconds
  */
-extern u64 __cputime_msec_factor;
+extern u64 __cputime_usec_factor;
 
 static inline unsigned long cputime_to_usecs(const cputime_t ct)
 {
-	return mulhdu(ct, __cputime_msec_factor) * USEC_PER_MSEC;
+	return mulhdu(ct, __cputime_usec_factor);
 }
 
 static inline cputime_t usecs_to_cputime(const unsigned long us)

@@ -143,7 +143,7 @@ static inline cputime_t usecs_to_cputime(const unsigned long us)
 	sec = us / 1000000;
 	if (ct) {
 		ct *= tb_ticks_per_sec;
-		do_div(ct, 1000);
+		do_div(ct, 1000000);
 	}
 	if (sec)
 		ct += (cputime_t) sec * tb_ticks_per_sec;

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 522bb1d..69477e5 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c

@@ -168,13 +168,13 @@ EXPORT_SYMBOL_GPL(ppc_tb_freq);
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING
 /*
  * Factors for converting from cputime_t (timebase ticks) to
- * jiffies, milliseconds, seconds, and clock_t (1/USER_HZ seconds).
+ * jiffies, microseconds, seconds, and clock_t (1/USER_HZ seconds).
  * These are all stored as 0.64 fixed-point binary fractions.
  */
 u64 __cputime_jiffies_factor;
 EXPORT_SYMBOL(__cputime_jiffies_factor);
-u64 __cputime_msec_factor;
-EXPORT_SYMBOL(__cputime_msec_factor);
+u64 __cputime_usec_factor;
+EXPORT_SYMBOL(__cputime_usec_factor);
 u64 __cputime_sec_factor;
 EXPORT_SYMBOL(__cputime_sec_factor);
 u64 __cputime_clockt_factor;

@@ -192,8 +192,8 @@ static void calc_cputime_factors(void)
 
 	div128_by_32(HZ, 0, tb_ticks_per_sec, &res);
 	__cputime_jiffies_factor = res.result_low;
-	div128_by_32(1000, 0, tb_ticks_per_sec, &res);
-	__cputime_msec_factor = res.result_low;
+	div128_by_32(1000000, 0, tb_ticks_per_sec, &res);
+	__cputime_usec_factor = res.result_low;
 	div128_by_32(1, 0, tb_ticks_per_sec, &res);
 	__cputime_sec_factor = res.result_low;
 	div128_by_32(USER_HZ, 0, tb_ticks_per_sec, &res);

-- 
1.7.8


-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Hi Andreas,

Commit d57af9b (taskstats: use real microsecond granularity for CPU
times) renamed msecs_to_cputime to usecs_to_cputime, but failed to
update all numbers on the way.  This causes nonsensical cpu
idle/iowait values to be displayed in /proc/stat (the only user of
usecs_to_cputime so far).

This also renames __cputime_msec_factor to __cputime_usec_factor,
adapting its value and using it directly in cputime_to_usecs instead
of doing two multiplications.

Thanks for finding this! I noticed the strange behaviour yesterday and
was just about to investigate.

Can I suggest we add: 

Cc: <redacted> [2.6.37+]

so it will make it back into the stable trees?

Anton

Signed-off-by: Andreas Schwab <redacted>

FWIW:
Acked-by: Anton Blanchard <redacted>

Anton Blanchard [off-list ref] writes:

Hi Andreas,

quoted

Commit d57af9b (taskstats: use real microsecond granularity for CPU
times) renamed msecs_to_cputime to usecs_to_cputime, but failed to
update all numbers on the way.  This causes nonsensical cpu
idle/iowait values to be displayed in /proc/stat (the only user of
usecs_to_cputime so far).

This also renames __cputime_msec_factor to __cputime_usec_factor,
adapting its value and using it directly in cputime_to_usecs instead
of doing two multiplications.

Thanks for finding this! I noticed the strange behaviour yesterday and
was just about to investigate.

Can I suggest we add: 

Cc: <redacted> [2.6.37+]

so it will make it back into the stable trees?

There is no user of usecs_to_cputime before 3.2-rc1, so it wouldn't have
any effect for older versions.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Hi Andreas,

There is no user of usecs_to_cputime before 3.2-rc1, so it wouldn't
have any effect for older versions.

Great, that explains why I only noticed it last week :)

Anton