Jan Kiszka wrote:
Philippe Gerum wrote:Here is likely why we have different levels of accuracy and performance, firstly my version is bluntly based on the khz freq, secondly it calculates the other way around, i.e. ns2tsc, so that tsc are keep in the inner code, but more efficiently converted from ns counts passed to the outer interface: static unsigned long ns2cyc_scale; #define NS2CYC_SCALE_FACTOR 10 /* 2^10, carefully chosen */ static inline void set_ns2cyc_scale(unsigned long cpu_khz) { ns2cyc_scale = (cpu_khz << NS2CYC_SCALE_FACTOR) / 1000000; } static inline unsigned long long ns_2_cycles(unsigned long long ns) { return ns * ns2cyc_scale >> NS2CYC_SCALE_FACTOR; }Your version performs ~50% better than mine (outperforming the original version by factor 7 on a 1 GHz box, vs. 4.8). I think you compared non-optimised code, didn't you?
Nah, I'm not that drunk! Without -O2, I see 15 times better
performance.
Redone the check here on a Centrino 1.6Mhz, and still have roughly x20 improvement (a bit better actually). I'm using Debian/sarge gcc 3.3.5.
[Gilles variant yet refuses the get benchmarked.] Jan
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