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From: Andrew Morton <akpm@linux-foundation.org>
To: Jonathan Lim <jlim@sgi.com>
Cc: linux-kernel@vger.kernel.org, jlan@sgi.com,
	"H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH] Provide u64 version of jiffies_to_usecs() in kernel/tsacct.c
Date: Wed, 2 Jan 2008 16:23:38 -0800	[thread overview]
Message-ID: <20080102162338.c67769af.akpm@linux-foundation.org> (raw)
In-Reply-To: <200801022103.m02L3oL1051764@sabah.engr.sgi.com>

On Fri, 28 Dec 2007 13:26:07 -0800 (PST) Jonathan Lim <jlim@sgi.com> 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.
> 
> Diff'd against: linux/kernel/git/stable/linux-2.6.23.y.git
> 
> Signed-off-by: Jonathan Lim <jlim@sgi.com>
> 
> --- a/kernel/tsacct.c	2007-12-28 11:58:05.182065029 -0800
> +++ b/kernel/tsacct.c	2007-12-28 11:57:37.949013675 -0800
> @@ -71,6 +71,17 @@ void bacct_add_tsk(struct taskstats *sta
>  
>  #ifdef CONFIG_TASK_XACCT
>  
> +static inline u64 jiffies_to_usecs_u64(const u64 j)
> +{
> +#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
> +	return (USEC_PER_SEC / HZ) * j;
> +#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
> +	return (j + (HZ / USEC_PER_SEC) - 1)/(HZ / USEC_PER_SEC);
> +#else
> +	return (j * USEC_PER_SEC) / HZ;
> +#endif
> +}
> +
>  #define KB 1024
>  #define MB (1024*KB)
>  /*
> @@ -81,8 +92,8 @@ 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_to_usecs_u64(p->acct_rss_mem1) * PAGE_SIZE / MB;
> +	stats->virtmem = jiffies_to_usecs_u64(p->acct_vm_mem1) * PAGE_SIZE / MB;
>  	mm = get_task_mm(p);
>  	if (mm) {
>  		/* adjust to KB unit */

Fair enough.  But I guess that new function should be a kernel-wide thing
because surely other users will turn up.

Peter has been working on the accuracy of some of these conversion
functions and might need to know about this change?

       reply	other threads:[~2008-01-03  0:25 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <200801022103.m02L3oL1051764@sabah.engr.sgi.com>
2008-01-03  0:23 ` Andrew Morton [this message]
2008-01-03  0:36   ` H. Peter Anvin
2008-01-03  1:06     ` Jonathan Lim
2008-01-03  1:13       ` H. Peter Anvin
2008-02-15  2:27 Jonathan Lim
     [not found] <no.id>
2008-01-08  1:04 ` Jonathan Lim
2008-02-19 20:52 ` Jonathan Lim
2008-02-19 21:25   ` Randy Dunlap
2008-02-20  2:17     ` Jonathan Lim
2008-02-20  3:52       ` Randy Dunlap
2008-02-25 22:27 ` Jonathan Lim
2008-03-12 23:53   ` Roman Zippel
2008-04-18 21:54 ` Jonathan Lim
  -- strict thread matches above, loose matches on Subject: below --
2007-12-28 21:26 Jonathan Lim
2007-12-29  4:52 ` H. Peter Anvin

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