More about Bulldozer

Further on the new AMD Bulldozer architecture, one will see that it is actually made up of blocks of 2 cores. Each of these is called a 'Bulldozer module', and each shares an L2 cache, an FPU, and more. When looking at it from this perspective, this will help people to understand why it is most efficient to *try* to keep the workload on every other core, if possible. Not only for TurboCore, but also due to the intrinsic properties of the platform.

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AMD Bulldozer hotfix appears - changes Scheduler awareness of CPU from X real cores to 1/2 X real cores

AMD Bulldozer hotfix appears - changes Scheduler awareness of CPU from X real cores to 1/2 X real cores

After appearing briefly a few weeks ago, then disappearing due to reported user complications, the AMD Bulldozer hotfixes for Windows have been re-released, or in the process of being re-released. A helpful supporter of Bitsum pointed this out. Over the course of the day, I noticed an additional download became available (at the first link).


This update DOES change the way the Windows sees your CPU, and can cause Process Lasso to deactivate under some scenarios. This is because it changes the CPU Scheduler's recognition of these AMD processors from (for example) 8 real cores to 4 real cores with 4 hyper-threaded (fake) cores. This is essentially a cheap hack to get performance on par and make use of TurboCore and the intrinsic characteristics of the Bulldozer architecture (e.g. shared L2 cache per 'module' of 2 cores) by telling the scheduler to keep its load on no more than 1/2 of the processors, if it can - and keep any large load off the other cores, if it can.


For example, before this update the below would read "[8 cores: 8 logical]". Meaning, 8 physical (real) cores, 8 total cores.

Now, as the reader can see, the OS thinks there are only 4 real cores, and 4 hyper-threaded (fake) cores. In this way, it is an easy and quick 'hack' to get the Scheduler to play nice with the Bulldozer platform and its 'paired' CPUs with shared L2 caches. Microsoft simply used the pre-existing support for HyperThreaded CPUs.


This will not hurt performance, it will help it. The other cores will get *fully* used under highly threaded situations, they are just avoided. These cores are also now frequently in a 'parked' state, so this update may conserve energy as well.

http://support.microsoft.com/kb/2645594
http://support.microsoft.com/kb/2646060

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