Re: [Xen-devel] cpufreq: weird bug in set_time_scale

[Jean Pihet <jpihet@xxxxxxxxxx>]

Keir,

On Thursday 11 October 2007 20:31:53 Keir Fraser wrote:
> Yep, that case is not acceptable for the DIV instruction, because it causes
> overflow of the quotient. It's fixed by xen-unstable changeset 16098.
>
> It's a one-char fix: the loop on (tps32 < MILLISECS(1000)) needs to be
> (tps32 <= MILLISECS(1000)).
Indeed that nicely fixes the problem.

>
>  -- Keir

Thanks,
Jean

>
> On 11/10/07 19:14, "Jean Pihet" <jpihet@xxxxxxxxxx> wrote:
> > Hi,
> >
> > The problem is in divl instruction which throws a 'Floating point
> > exception'. In the case below the dividend and the divisor are equal. Is
> > that allowed by the instruction?
> >
> > On the ARM code that we are currently implementing, there is no crash
> > =;-) but the result is 0, which does not seem correct.
> >
> > Should the assert in div_frac be changed to avoid weird results or crash?
> >
> > Regards,
> > Jean
> >
> > On Thursday 11 October 2007 19:43:08 Keir Fraser wrote:
> >> That's my code. I'll take a look!
> >>
> >>  K.
> >>
> >> On 11/10/07 16:55, "Langsdorf, Mark" <mark.langsdorf@xxxxxxx> wrote:
> >>> On my test machine, in set_time_scale(),
> >>> the following code:
> >>> ts->mul_frac = div_frac(MILLISECS(1000), tps32);
> >>> crashes with a division by zero error if
> >>> tps32 == 1000000000d.  Unfortunately, tps32 is
> >>> often that value.
> >>>
> >>> Does anyone know why this happens?  I've
> >>> resolved it temporarily by checking for
> >>> tps32 == 1000000000 and changing the
> >>> value slightly (101000010d works fine
> >>> on my test machine), but I'm not sure
> >>> if that's the approved approach for Xen.
> >>>
> >>> -Mark Langsdorf
> >>> Operating System Research Center
> >>> AMD
> >>>
> >>>
> >>>
> >>> _______________________________________________
> >>> Xen-devel mailing list
> >>> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >>> http://lists.xensource.com/xen-devel
> >>
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >> http://lists.xensource.com/xen-devel



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