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

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 

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