From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Tue, 13 Jun 2006 19:04:34 +0200
From: Philippe Gerum <rpm@xenomai.org>
MIME-Version: 1.0
Subject: Re: [Xenomai-core] ns vs. tsc as internal timer base
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To: Jan Kiszka <jan.kiszka@domain.hid>
Cc: xenomai-core <xenomai@xenomai.org>

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
> 


-- 

Philippe.