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On 20 Jun 2005 at 14:10, Lee Revell wrote: > On Mon, 2005-06-20 at 10:09 -0700, john stultz wrote: > > As for gettimefoday() syscall performance, I one had some numbers, but > > I > > would need to re-create them. I'll see if I can grab a slower box and > > give you some hard numbers. > > I ran some tests lately that showed gettimeofday() to be 50x slower than > rdtsc() on my 600Mhz machine. Many userspace apps that need a cheap Hello! Isn't that a kind of absurd comparison: rdtsc is one or two instructions, while gettimeofday is a complete syscall with some many instructions: rdtsc will never give you the time of day besides of that. Are you voting for replacing gettimeofday with rdtsc? > high res timer have to use rdtsc now due to the excessive overhead of > gettimeofday(). It would be more correct if these apps could use You can either have it accurate, or you can have it fast. Also gettimeofday works on any UNIX platform, rdtsc does not. > gettimeofday() for various reasons (cpufreq and SMP issues). Good point, but you don't get that higher reliability and accuracy for free. > > So this patch is addressing a real problem. I'd be interested to see if > the performance is good enough to replace rdtsc in these cases. In which applications (Java excepted maybe) do you really need to call gettimeofday more than a few thousand times per second? Most likely you are working around a different issue then. Regards, Ulrich - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | ||||||||||
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