Messages in this thread | | | Date | Thu, 29 Oct 2009 14:13:50 +0200 | From | Avi Kivity <> | Subject | Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation |
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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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