On Wed Jan 2 16:36:47 2008, [EMAIL PROTECTED] wrote:
>
> Andrew Morton wrote:
> > On Fri, 28 Dec 2007 13:26:07 -0800 (PST) Jonathan Lim <[EMAIL PROTECTED]>
> > 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 <[EMAIL PROTECTED]>
> >>
> >> --- 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?
>
> Yes, the function should be coded using the new #defines produced by
> timeconst.h; that way you end up avoiding a possible overflow in the
> multiplication.
>
> I believe all three cases can be folded, then, to:
>
> return (j*HZ_TO_USEC_NUM + HZ_TO_USEC_DEN-1) / HZ_TO_USEC_DEN;
>
> I would also like to observe that the roundoff behaviour of the function
> above is inconsistent; in case 2 it will round up, but in case 3 it
> will round down. The line proposed above has round up behaviour.
>
> -hpa
Peter,
Would you be willing to include the u64 function as part of your patch to make
it available kernel-wide? It just needs:
u64 inline jiffies_to_usecs_u64(const u64 j)
and for the symbol to be exported. Thanks.
Jonathan
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