Re: [PATCH] Provide u64 version of jiffies_to_usecs() in kernel/tsacct.c

Jonathan Lim
2008-04-18T21:54:00Z

It's possible that the values used in and returned from jiffies_to_usecs() are
incorrect because of truncation when variables of type u64 are involved. So a
function specific to that type is used instead.

This version implements a correction to jiffies_64_to_usecs() based on feedback
from Randy Dunlap and Roman Zippel.

Diff'd against: linux/kernel/git/torvalds/linux-2.6.git

Signed-off-by: Jonathan Lim <jlim@sgi.com>

--- a/include/linux/jiffies.h Thu Feb 14 18:04:14 PST 2008
+++ b/include/linux/jiffies.h Thu Feb 14 18:07:17 PST 2008
@@ -42,7 +42,7 @@
/* LATCH is used in the interval timer and ftape setup. */
#define LATCH ((CLOCK_TICK_RATE + HZ/2) / HZ) /* For divider */

-/* Suppose we want to devide two numbers NOM and DEN: NOM/DEN, then we can
+/* Suppose we want to divide two numbers NOM and DEN: NOM/DEN, then we can
* improve accuracy by shifting LSH bits, hence calculating:
* (NOM << LSH) / DEN
* This however means trouble for large NOM, because (NOM << LSH) may no
@@ -204,7 +204,7 @@ extern unsigned long preset_lpj;
* operator if the result is a long long AND at least one of the
* operands is cast to long long (usually just prior to the "*" so as
* not to confuse it into thinking it really has a 64-bit operand,
- * which, buy the way, it can do, but it takes more code and at least 2
+ * which, by the way, it can do, but it takes more code and at least 2
* mpys).

* We also need to be aware that one second in nanoseconds is only a
@@ -269,6 +269,7 @@ extern unsigned long preset_lpj;
*/
extern unsigned int jiffies_to_msecs(const unsigned long j);
extern unsigned int jiffies_to_usecs(const unsigned long j);
+extern u64 jiffies_64_to_usecs(const u64 j);
extern unsigned long msecs_to_jiffies(const unsigned int m);
extern unsigned long usecs_to_jiffies(const unsigned int u);
extern unsigned long timespec_to_jiffies(const struct timespec *value);
--- a/kernel/time.c Thu Feb 14 18:05:12 PST 2008
+++ b/kernel/time.c Fri Apr 18 14:44:54 PDT 2008
@@ -38,6 +38,7 @@

#include <asm/uaccess.h>
#include <asm/unistd.h>
+#include <asm/div64.h>

#include "timeconst.h"

@@ -267,6 +268,16 @@ unsigned int inline jiffies_to_usecs(con
#endif
}
EXPORT_SYMBOL(jiffies_to_usecs);
+
+u64 jiffies_64_to_usecs(const u64 j)
+{
+# if BITS_PER_LONG == 32
+ return ((u64)HZ_TO_USEC_MUL32 * j) >> HZ_TO_USEC_SHR32;
+# else
+ return div64_64(j*HZ_TO_USEC_NUM + HZ_TO_USEC_DEN-1, HZ_TO_USEC_DEN);
+# endif
+}
+EXPORT_SYMBOL(jiffies_64_to_usecs);

/**
* timespec_trunc - Truncate timespec to a granularity
--- a/kernel/tsacct.c Thu Feb 14 18:06:17 PST 2008
+++ b/kernel/tsacct.c Thu Feb 14 18:08:47 PST 2008
@@ -85,8 +85,8 @@ void xacct_add_tsk(struct taskstats *sta
struct mm_struct *mm;

/* convert pages-jiffies to Mbyte-usec */
- stats->coremem = jiffies_to_usecs(p->acct_rss_mem1) * PAGE_SIZE / MB;
- stats->virtmem = jiffies_to_usecs(p->acct_vm_mem1) * PAGE_SIZE / MB;
+ stats->coremem = jiffies_64_to_usecs(p->acct_rss_mem1) * PAGE_SIZE / MB;
+ stats->virtmem = jiffies_64_to_usecs(p->acct_vm_mem1) * PAGE_SIZE / MB;
mm = get_task_mm(p);
if (mm) {
/* adjust to KB unit */