Re: [Qemu-devel] [PATCH 2/2] [RFC] time: refactor QEMU timer to use GHRTimer

[Anthony Liguori <aliguori@us.ibm.com>]

On 08/23/2011 02:43 AM, Paolo Bonzini wrote:
> On 08/22/2011 09:21 PM, Anthony Liguori wrote:
>> - ticks = cpu_get_real_ticks();
>> - if (timers_state.cpu_ticks_prev > ticks) {
>> - /* Note: non increasing ticks may happen if the host uses
>> - software suspend */
>> - timers_state.cpu_ticks_offset += timers_state.cpu_ticks_prev - ticks;
>> - }
>> + ticks = get_clock();
>>
>> [...]
>>
>> -static inline int64_t cpu_get_real_ticks(void)
>> -{
>> - int64_t val;
>> - asm volatile ("rdtsc" : "=A" (val));
>> - return val;
>> -}
>> -
>
> cpu_get_ticks is used also to emulate the guest TSC, are you sure you
> want to change that uniformly to a 1 GHz rate?

Where possible, CLOCK_MONOTONIC_RAW should be implemented in terms or 
rdtscp.  It will provide the highest accuracy time source that you can get.

So I don't think there's any different in terms of timer granularity 
from using CLOCK_MONOTONIC_RAW and rdtsc directly other than the former 
is more correct.

Regards,

Anthony Liguori

>
> I had some more cleanups in this area, I'll try to get them tested and
> submitted but I have little time for this right now.
>
> Paolo