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

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Date:	Tue, 19 Feb 2008 19:52:01 -0800
From:	Randy Dunlap <randy.dunlap@...cle.com>
To:	Jonathan Lim <jlim@....com>
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH] Provide u64 version of jiffies_to_usecs() in kernel/tsacct.c

Jonathan Lim wrote:
> 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.
> 
> Diff'd against: linux/kernel/git/torvalds/linux-2.6.git
> 
> Signed-off-by: Jonathan Lim <jlim@....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	Tue Feb 19 17:00:11 PST 2008

kernel/time.c needs:
#include <asm/div64.h>

After that, it's
Acked-by: Randy Dunlap <randy.dunlap@...cle.com>

> @@ -268,6 +268,12 @@ unsigned int inline jiffies_to_usecs(con
>  }
>  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);
> +}
> +EXPORT_SYMBOL(jiffies_64_to_usecs);
> +
>  /**
>   * timespec_trunc - Truncate timespec to a granularity
>   * @t: Timespec
> --- 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 */


-- 
~Randy
--
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