Messages in this thread | | | From | "Lee Revell" <> | Subject | Re: Accessing monotonic clock from modules | Date | Fri, 3 Jun 2005 23:27:17 -0400 |
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> 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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