On 08/10/2012 11:10 AM, Gerd Hoffmann wrote:
> Hi,
>
>>>> >>> (1) Use this patch (with alignment issue fixed of course).
>>>> >>> (2) Do a full kvmclock implementation. Feels a bit like overkill.
>>>> >>> (3) SeaBIOS can fallback to the PIT for timing on machines which
>>>> >>> have no TSC. We could do that too in case we detect kvm ...
>>> >>
>>> >> What sort of timeouts are these? If seconds, maybe the rtc would be best.
>> >
>> > I vote for 3 so nobody has to maintain kvmclock code in SeaBIOS and Gerd
>> > can fix the in-kernel PIT issues with GRUB (see Michaels message) while testing.
> (2) turned out to be not too bad when taking a shortcut: Go through an
> enable/disable cycle each time we read the clock, then just grab
> system_time. Not that efficient, but should be ok for seabios. Usually
> it checks the clock when sitting around idle, waiting for something to
> happen. And it simplifies the implementation alot as we can just skip
> all the tsc frequency & delta calculations.
>
> Draft patch attached. Comments?
>
> +
> +static void kvmclock_fetch(struct pvclock_vcpu_time_info *time)
> +{
> + u32 addr = (u32)MAKE_FLATPTR(GET_SEG(SS), time);
> + u32 msr = GET_GLOBAL(kvm_systime_msr);
> +
> + memset(time, 0, sizeof(*time));
> + wrmsr(msr, addr | 1);
I'd put the time calculations in here. We don't specify what happens to
the data area after disabling kvmclock; it could be in the middle of an
update.
> + wrmsr(msr, 0);
> +}
> +
> +u64 kvmclock_get(void)
> +{
> + struct pvclock_vcpu_time_info time;
> +
> + kvmclock_fetch(&time);
> + return time.system_time;
That's just a random number. You have to do the full calculation.
--
error compiling committee.c: too many arguments to function
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