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@lists.xensource.com http://lists.xensource.com/xen-devel
That''s my code. I''ll take a look! K. On 11/10/07 16:55, "Langsdorf, Mark" <mark.langsdorf@amd.com> 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@lists.xensource.com > http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
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@amd.com> 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@lists.xensource.com > > http://lists.xensource.com/xen-devel > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
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)). -- Keir On 11/10/07 19:14, "Jean Pihet" <jpihet@mvista.com> 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@amd.com> 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@lists.xensource.com >>> http://lists.xensource.com/xen-devel >> >> _______________________________________________ >> Xen-devel mailing list >> Xen-devel@lists.xensource.com >> http://lists.xensource.com/xen-devel > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
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.> > -- KeirThanks, Jean> > On 11/10/07 19:14, "Jean Pihet" <jpihet@mvista.com> 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@amd.com> 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@lists.xensource.com > >>> http://lists.xensource.com/xen-devel > >> > >> _______________________________________________ > >> Xen-devel mailing list > >> Xen-devel@lists.xensource.com > >> http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
Langsdorf, Mark
2007-Oct-11 19:45 UTC
RE: [Xen-devel] cpufreq: weird bug in set_time_scale
> 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)).Thanks, that fixed it. -Mark Langsdorf Operating System Research Center AMD _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel