Re: kvm-37 problem w/ 64-bit division in lapic.c

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Jindrich Makovicka wrote:
> On Mon, 10 Sep 2007 11:49:02 +0200
> "Jindrich Makovicka" <makovick-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>   
>> On 9/10/07, Dong, Eddie <eddie.dong-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
>>     
>>> div64_32 is enough, does this function exist?
>>>       
>> afaik, __div64_32 is architecture specific, but do_div() could be
>> actually used here.
>>     
>
> This version should be faster.
>
>   

[please don't post patches with extensions like ".diff2", which don't 
show in the mail reader]

> -       u32 counter_passed;
> +       u64 counter_passed;
>         ktime_t passed, now = apic->timer.dev.base->get_time();
>         u32 tmcct = apic_get_reg(apic, APIC_TMICT);
>
> @@ -512,8 +512,8 @@ static u32 apic_get_tmcct(struct kvm_lapic *apic)
>         } else
>                 passed = ktime_sub(now, apic->timer.last_update);
>
> -       counter_passed = div64_64(ktime_to_ns(passed),
> -                                 (APIC_BUS_CYCLE_NS * 
> apic->timer.divide_count));
> +       counter_passed = ktime_to_ns(passed);
> +       do_div(counter_passed, APIC_BUS_CYCLE_NS * 
> apic->timer.divide_count);
>         tmcct -= counter_passed;

What if counter_passed overflows?  Sure, that means kvm wasn't scheduled 
for 4 seconds, but it could happen.


-- 
error compiling committee.c: too many arguments to function


-------------------------------------------------------------------------
This SF.net email is sponsored by: Microsoft
Defy all challenges. Microsoft(R) Visual Studio 2005.
http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/