Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation

Avi Kivity
2009-10-28T05:52:55Z

On 10/27/2009 08:20 PM, Jeremy Fitzhardinge wrote:
> On 10/27/09 10:29, Dan Magenheimer wrote:
>
>> Is there any way for an application to conclusively determine
>> programmatically if the "fast vsyscall" pvclock is functional
>> vs the much much slower gettimeofday/clock_gettime equivalents?
>>
>> If not, might it be possible to implement some (sysfs?)
>> way to determine this, that would also be backwards compatible
>> to existing OS's that don't have pvclock+vsyscall supported?
>>
>>
> It would probably be simplest and most portable for the app to just
> measure the performance of gettimeofday and see if it meets its needs.
>

How can you reliably measure performance in a virtualized environment?

--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.