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[ iometer-Bugs-1344273 ] Incorrect performance results on mobile platforms

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[ iometer-Bugs-1344273 ] Incorrect performance results on mobile platforms

SourceForge.net
Bugs item #1344273, was opened at 2005-10-31 20:52
Message generated for change (Tracker Item Submitted) made by Item Submitter
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https://sourceforge.net/tracker/?func=detail&atid=427254&aid=1344273&group_id=40179

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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: John Winfield (winfij)
Assigned to: Nobody/Anonymous (nobody)
Summary: Incorrect performance results on mobile platforms

Initial Comment:
I've been getting incorrect throughput results on my
laptop to a USB drive and wading through the source
code I found that you're using the RDTSC to calculate
the runtime for use in getting the MB/s throughput.
This won't work on mobile platforms since they change
clock speed dynamically and thus report a fixed RDTSC
rate independant of the CPU clock speed.

There's a note about this from the NVIDIA web site:

Don't use the Read Time Stamp Counter (RDTSC) to do
timing in your app. Here's why: it is unusable on mobile
platforms because calculations assume a fixed clock
speed. Mobile platforms (such as notebooks) will
throttle back the CPU at unexpected times making the
tick count from RDTSC useless. Instead use
QueryPerformanceCounter, which insures consistent
architecture independent results.


Hope that helps you sort it.

Cheers,

John


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