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Old 10-10-11, 10:41 PM   #107
Ninja Prime
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Join Date: Mar 2003
Location: Utah
Posts: 2,263
Default Re: Sigh- Bulldozer fail prediction from AMD staff

Originally Posted by nekrosoft13 View Post
i would like to see more info about that "bug" is it similar screwup like they had they had before with 9x00 series? and few months later they releaed 9x50 series with a fix.
Heres the quote I read:

Actually, we already have such an issue known for Bulldozer, and NO bench-marked system has the patch installed!

The shared L1 cache is causing cross invalidations across threads so that the prefetch data is incorrect in too many cases and data must be fetched again. The fix is a "simple" memory alignment and (possible)tagging system in the kernel of Windows/Linux.

I reviewed the code for the Linux patch and was astonished by just how little I know of the Linux kernel... lol! In any event, it could easily cost 10% in terms of single threaded performance, possibly more than double that in multi-threaded loads on the same module due to the increased contention and randomness of accesses.
Basically a bug in the two cores sharing one L1 cache, and the operating system not understanding it, so it has to fetch the data twice most of the time.
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