Arjan van de Ven wrote:
On Thu, 2005-06-02 at 07:46 -0600, Chris Friesen wrote:
For ourselves we implemented an clock interface for a limited subset of
architectures that provides a fast timestamp in kernel and userspace.
Basically it has one call to return a 64-bit timestamp, and another call
to tell you how fast the clock is ticking.
hmm this is tricky if cpufreq actually varies cpu speeds... you would
need to not cache the "how fast it ticks" for too long.
Luckily we didn't need to deal with that.
In order to use the fast versions with varying frequency you'd need some
kind of notification to all users when the frequency changes.
Alternately, on architectures where clock_gettime doesn't require the
overhead of a syscall, you could just use that.
JACK also implements a fast high-res timer for each supported arch. We
can't use gettimeofday as it's about 50x slower than rdtsc (tested it just
now).
I suggested using the kernel events mechanism to notify userspace when
the CPU speed changes a few months ago, for this exact reason.
Lee
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