Re: [Algorithms] Timing problems

[Jon W. <jw...@gm...>]

Paul at Home wrote:
> I've just fallen foul of QPC not working correctly having just gone 
> from a single processor to a quad core.
>  
> I remember reading somewhere that multiple processors could cause 
> problems in the future, but I guess the future (for me) just arrived. 
> I do handle the well-known "jump" problem but I guess that's old news 
> now anyway.
>  
> Can anyone point me in the right direction for how to fix this please ?


There are two fixes:

1) Keep the last value returned, and return max(lastValue, nextValue). 
Requires some degree of locking or compare/exchange to work in a 
multi-threaded fashion, or using TLS for the "lastValue".

2) Install proper CPU drivers for your system so you don't get 
incoherent results. <-- vastly preferred method

Sincerely,

jw