Giovanni Bajo wrote: > Hello, > > I experimented something very strange, a few days ago. I was debugging an > application at a customer's site, and the problem turned out to be that > time.clock() was going "backwards", that is it was sometimes (randomically) > returning a floating point value which was "less than" the value returned by > the previous invokation. The computer was a pretty fast one (P4 3Ghz I think, > running Windows XP), and this happened only between very close invokations of > time.clock(). > > I have triple-verified this, including printing the repr() of the floating > point number and verifying it was really minor than the previous value by a > few > microseconds. In other words, I'm absolutely positive that it's not a mistake > on my side, but that time.clock() was really apparently "jumping backward". > This was confusing the hell out of my application, of course, and I just > hacked > it so to ignore these bogus reads, and just reading off again. Since the error > was just of a few microseconds, reading time.clock() again produces a number > which was higher than what I had before, and thus OK for my application. > > I was wondering if someone had experimented this behaviour before. I tried > googling but to no effect. Is it possible this to be a bug in Python itself > (maybe, shooting at the moon, in the conversion between the 64bit performance > counter and the floating point representation returned by time.clock()), or > could it be a bug in Windows itself or the mother board drivers (buf if so, > wouldn't other application start going mad)?
From the MSDN docs for QueryPerformanceCounter: Remarks: On a multiprocessor computer, it should not matter which processor is called. However, you can get different results on different processors due to bugs in the basic input/output system (BIOS) or the hardware abstraction layer (HAL). To specify processor affinity for a thread, use the SetThreadAffinityMask function. Are you running on a multi-core or a multi-processor machine? The best way to handle this is probably to make your application 'tolerant' to such cases. [sreeram;]
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