SecondLevelDataCache Tweak

[carloc]

From this site:

Myth - "Adjusting the SecondLevelDataCache Registry value to match your CPU's L2 Cache size will improve performance."

Reality - "If you do not set this registry value, Windows will use the HAL (Hardware Abstraction Layer) for retrieval of the L2 cache size automatically on boot up. If this fails, a default value of 256KB is used. This is where the myth that XP can only use 256KB of L2 cache comes from. But it's false. The SecondLevelDataCache is designed as a secondary source of cache size information for computers on which the HAL cannot detect the L2 cache. The HAL is able to retrieve the L2 cache size from any CPU using the set-associative cache design (Pentium II or newer), it's only the relatively few older processors with direct-mapped L2 caches that the HAL will not recognize. This tweak only applies to older computers (Pentium I or older) with over 64MB of memory. On these older systems, this tweak can improve performance by about 0.4%. Pentium II and later CPUs are not affected." Source

What do you think about it?
I just changed my value to 512 but I've not seen any difference.

[Curio]

Did you not read your own post?

[carloc]

Sure I read my post I was a bit incomplete really...
I tried to change that value because I found that SecondLevelDataCache was set to 0 (zero) and it seems strange to me...
If everything is ok for my P4, why SecondLevelDataCache is not set to 512 (or to the default value 256)??

[oftentired]

There is nothing wrong with it being set to zero. Nothing wrong with changing it to 256 or 512 either.

SecondLevelDataCache records the size of the processor cache, also known as the secondary or L2 cache. If the value of this entry is 0, the system attempts to retrieve the L2 cache size from the Hardware Abstraction Layer (HAL) for the platform. If it fails, it uses a default L2 cache size of 256 KB. If the value of this entry is not 0, it uses this value as the L2 cache size. This entry is designed as a secondary source of cache size information for computers on which the HAL cannot detect the L2 cache.

in other words when it is set to zero it forces another attempt to use HAL to retrieve the cache size before defaulting to 256.

My above quote is from Microsoft KB Detailed Explanation of SecondLevelDataCache