linux-kernel - Re: [PATCH] Provide u64 version of jiffies_to

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Date:	Mon, 7 Jan 2008 17:04:08 -0800 (PST)
From:	Jonathan Lim <jlim@....com>
To:	linux-kernel@...r.kernel.org
Cc:	hpa@...or.com, akpm@...ux-foundation.org, jlan@....com
Subject: Re: [PATCH] Provide u64 version of jiffies_to_usecs() in kernel/tsacct.c

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.

Updated from previous submission with feedback from Peter Anvin.

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

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

--- a/include/linux/jiffies.h	2008-01-07 16:09:17.737040981 -0800
+++ b/include/linux/jiffies.h	2008-01-07 16:09:17.693033003 -0800
@@ -36,7 +36,7 @@
 /* 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
@@ -198,7 +198,7 @@ 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
@@ -263,6 +263,7 @@ 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	2008-01-07 16:09:17.841059839 -0800
+++ b/kernel/time.c	2008-01-07 16:09:17.825056938 -0800
@@ -267,6 +267,12 @@ unsigned int inline jiffies_to_usecs(con
 }
 EXPORT_SYMBOL(jiffies_to_usecs);
 
+u64 inline jiffies_64_to_usecs(const u64 j)
+{
+	return (j*HZ_TO_USEC_NUM + HZ_TO_USEC_DEN-1) / HZ_TO_USEC_DEN;
+}
+EXPORT_SYMBOL(jiffies_64_to_usecs);
+
 /**
  * timespec_trunc - Truncate timespec to a granularity
  * @t: Timespec
--- a/kernel/tsacct.c	2008-01-07 16:09:17.833058389 -0800
+++ b/kernel/tsacct.c	2008-01-07 16:09:17.793051136 -0800
@@ -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 */
--
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