Re: [PATCH 2/2] x86/HVM: Use fixed TSC value when saving or restoring domain

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

On 03/31/2014 10:34 AM, Jan Beulich wrote:
>
>>>> index 95b4b91..032eb23 100644
>>>> --- a/xen/include/xen/time.h
>>>> +++ b/xen/include/xen/time.h
>>>> @@ -32,7 +32,8 @@ struct vcpu;
>>>>    typedef s64 s_time_t;
>>>>    #define PRI_stime PRId64
>>>>    
>>>> -s_time_t get_s_time(void);
>>>> +s_time_t get_s_time_fixed(u64 at_tick);
>>>> +#define get_s_time() get_s_time_fixed(0)
>>> get_s_time(), through NOW(), has quite many users, so I'm not certain
>>> the code bloat resulting from this is desirable. I'd suggest the function
>>> to remain such; the compiler will be able to make it a mov+jmp.
>> Sorry, not sure I understand what you are asking for.
>>
>> There shouldn't be much of code size increase since get_s_time()
>> currently (and get_s_time_fixed() after this patch is applied) are not
>> inlines. The only increase is due to routine itself getting very
>> slightly larger.
>>
>> But I suspect you meant something else.
> All call sites have to zero %edi with the change in place, and I
> was trying to tell you that the number of call sites of this isn't
> exactly small due to the function's use via NOW(). Hence I think
> you shouldn't penalize the callers and have an explicit out of line
> wrapper.

OK, I understand the concern now but still confused about what you want ;-(

Two separate routines that only differ in how tsc is calculated (rdtscll 
vs. an 'in' parameter)?

-boris