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

Randy Dunlap
2008-02-19T21:26:42Z

On Tue, 19 Feb 2008 12:52:46 -0800 (PST) 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.
>
> 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 Tue Feb 19 12:44:03 PST 2008
> @@ -268,6 +268,14 @@ unsigned int inline jiffies_to_usecs(con
> }
> EXPORT_SYMBOL(jiffies_to_usecs);
>
> +u64 inline jiffies_64_to_usecs(const u64 j)
> +{
> + u64 tmp = j*HZ_TO_USEC_NUM + HZ_TO_USEC_DEN-1;
> + do_div(tmp, HZ_TO_USEC_DEN);

do_div() is:
* The semantics of do_div() are:
*
* uint32_t do_div(uint64_t *n, uint32_t base)

Maybe you want div64_64().

> + return tmp;
> +}
> +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