Jan Kiszka wrote: > Gilles Chanteperdrix wrote: >> Jan Kiszka wrote: >>> Jan Kiszka wrote: >>> >>>> Jan Kiszka wrote: >>>> ... >>>> >>>>> fast-tsc-to-ns-v2.patch >>>>> >>>>> [Rebased, improved rounding of least significant digit] >>>> Rounding in the fast path for the sake of the last digit was silly. >>>> Instead, I'm now addressing the ugly interval printing via >>>> xnarch_precise_tsc_to_ns when converting the timer interval back into >>>> nanos. -v3 incorporating this has just been uploaded. >>>> >>> After noticing yesterday that even unpatched Xenomai sometimes converts >>> inaccurately when showing small timer intervals under /proc, I just got >>> an idea how to address this beautification issue even better: -v4 now >>> rounds up in the slow, precise tsc-to-ns path, see >>> >>> http://www.rts.uni-hannover.de/rtaddon/patches/xenomai/fast-tsc-to-ns-v4.patch >> I am the one who decided of the rounding behaviour of llimd, RTAI >> version had the same rounding policy as the one you propose, and I made >> it for the following reasons: >> - rouding towards 0 is the policy used by the C language, so doing this >> for llimd made it consistent with what one expects from C code; >> - values computed by llimd are used to program timers, and we prefer the >> timer to be programmed for a too short value than for a too long value. > > That's OK, I agree. In my patch for i386, this rounding is only relevant > for display purposes. It's just to help me finding the expected period T > of my task in /proc instead of T-1 sometimes. Beautification. All we > need for other archs is xnarch_tsc_to_ns according to the old scheme. > Will rework this.
Done, -v5 is online. This is not yet incorporating any change to the generic llmulshft. I haven't thought about nor tried our code on a 64 bit arch yet. Did you check this already? I wonder, eg., if it makes sense to exploit 128 bit with 64 bit shifts there or stick with 94/32 bit accuracy and related conversion errors. Depending on this, the generic version might have to be reconsidered. Jan
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