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

On 10/28/2009 07:47 PM, Jeremy Fitzhardinge wrote:
Much better to have an API for this.  Life is hacky enough already.
My point is that if an app cares about property X then it should just
measure property X.  The fact that gettimeofday is a vsyscall is just an
implementation detail that apps don't really care about.  What they care
about is whether gettimeofday is fast or not.

But we can not make a reliable measurement.

If the environment has such unstable timing that the effect can't be
measured, then it is moot whether its a vsyscall or not (but in that
case its almost certainly better to use the standard API rather than
trying to roll your own timesource with rdtsc).

If you're interested in gettimeofday() for a global monotonic counter you can fall back to atomic_fetch_and_add() which will be faster than a syscall even on large systems. Maybe we should provide a vsyscall for global monotonic counters and implement it using a atomics or tsc instead of these hacks (I'm assuming here that the gettimeofday() calls are used to implement an atomic counter - are they?)

error compiling committee.c: too many arguments to function

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