Subject: Re: [RFC/PATCH v4 1/3] add high resolution timer function to debug performance issues

From: Karsten Blees <[email-masked]>
Date: Wed, 21 May 2014 11:14:16 +0200

Am 21.05.2014 09:31, schrieb Noel Grandin:
> On 2014-05-20 21:11, Karsten Blees wrote:
>>   * implement Mac OSX version using mach_absolute_time
>>
>>
> 
> 
> Note that unlike the Windows and Linux APIs, mach_absolute_time does not do correction for frequency-scaling

I don't have a MAC so I can't test any of this, but supposedly mach_timebase_info() returns the frequency of mach_absolute_time(), so you could do similar frequency-scaling as I do for Windows with QueryPerformanceFrequency().

> and cross-CPU synchronization with the TSC.
> 

The TSC is synchronized across cores and sockets on modern x86 hardware [1] (at least since Intel Nehalem, i.e. all Core i[357] processors). On older machines, I would expect the OS API to choose a more appropriate time source, e.g. the HPET. I'm not proposing to use asm("rdtsc") or anything like that...

[1] https://software.intel.com/en-us/articles/best-timing-function-for-measuring-ipp-api-timing

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