Just to let you know

Hi all

Bought my fave hardware magazine the other day and discovered something
which I thought others might want to know about ( just in case ).

A lot of people these days are running processors with a fast L2 cache,
normally 512kb - Northwood or Bartons for example. Did you kow that if you
are running XP you will only be using 256Kb of this at the most as XP is
only configured to utilise that amount. If you are running a 512Kb L2 Cache
or higher you need to register it manually.

You can do this by going to
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\SessionManager\MemoryMan
agement and find the DWORD entry : SecondLevelDataCache. When entering
values here, be sure to use the correct numeric system. 256Kb should be
entered as 100 in hexadecimal, 512Kb is 200 and 1024Kb is 400

Hope this is of use to some of you guys and gals

Peace

Daniel

From the horse's mouth (Microsoft):

Begin quote.....

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.

This is not related to the hardware; it is only useful for computers with
direct-mapped L2 caches. Pentium II and later processors do not have direct-
mapped L2 caches. SecondLevelDataCache can increase performance by
approximately 2 percent in certain cases for older computers with ample
memory (more than 64 MB) by scattering physical pages better in the address
space so there are not so many L2 cache collisions. Setting
SecondLevelDataCache to 256 KB rather than 2 MB (when the computer has a 2
MB L2 cache) would probably have about a 0.4 percent performance penalty.

End quote....

Seems to me that unless you're running a P2 or older that this is a
non-issue.


"Daniel Yates" wrote in message
...
Hi all

Bought my fave hardware magazine the other day and discovered something
which I thought others might want to know about ( just in case ).

A lot of people these days are running processors with a fast L2 cache,
normally 512kb - Northwood or Bartons for example. Did you kow that if you
are running XP you will only be using 256Kb of this at the most as XP is
only configured to utilise that amount. If you are running a 512Kb L2
Cache
or higher you need to register it manually.

You can do this by going to

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Contro l\SessionManager\MemoryMan
agement and find the DWORD entry : SecondLevelDataCache. When entering
values here, be sure to use the correct numeric system. 256Kb should be
entered as 100 in hexadecimal, 512Kb is 200 and 1024Kb is 400

Hope this is of use to some of you guys and gals

Peace

Daniel

"Frank Weston" wrote in message
...
From the horse's mouth (Microsoft):

Begin quote.....

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.

This is not related to the hardware; it is only useful for computers with
direct-mapped L2 caches. Pentium II and later processors do not have
direct-
mapped L2 caches. SecondLevelDataCache can increase performance by
approximately 2 percent in certain cases for older computers with ample
memory (more than 64 MB) by scattering physical pages better in the
address
space so there are not so many L2 cache collisions. Setting
SecondLevelDataCache to 256 KB rather than 2 MB (when the computer has a 2
MB L2 cache) would probably have about a 0.4 percent performance penalty.

End quote....

Seems to me that unless you're running a P2 or older that this is a
non-issue.

snip

Setting the SecondLevelDataCache to 2MB??? Thats seems a very high value to
me?

Either way I am not 100% clued up no the actions of L2 but your post has
helped a little. thought I would share the article as when I checked my
setting on a P4 1.7Ghz there was no value at all.

Regards

Daniel Yates

Your Pentium 4 1.7 GHz has a 256 Kbyte L2 cache. Later Pentium 4 CPU's have
512 Kbytes L2 cache. Pentium 4 class Celeron CPU's have 256 Kbytes L2
cache. Xeon CPU's have up to two Mbytes L2 cache. The L2 cache stores
information that was last used by the CPU, in blocks that are tied to the
actual main memory address. Since code is generally contiguous, and data
tends to be contiguous, this provides a speedy response to memory contents
access in most cases, greatly reducing the effect of memory latency.
Depending on the task and how the code is written, an L2 cache can more than
double the throughput. One example is the client for SETI@home... a CPU
with a 2 Mbyte L2 cache processes a work unit much faster than the same CPU
type and clock speed with a 512 Kbyte L2 cache. Part of this difference
could be eliminated if the code were rewritten to use a smaller L2 cache
efficiently. For some other applications the L2 cache makes little
noticable difference. The L2 cache is an attempt to bridge between the very
fast CPU clock speed and multiple instruction execution per clock cycle and
the slower memory clock. The greater the difference the more the L2 cache
helps.

SySoft Sandra has a test module that graphically shows the effect L2 cache
size vs. code and data block size.

Phil Weldon,

"Daniel Yates" wrote in message
...

"Frank Weston" wrote in message
...
From the horse's mouth (Microsoft):

Begin quote.....

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.

This is not related to the hardware; it is only useful for computers
with
direct-mapped L2 caches. Pentium II and later processors do not have
direct-
mapped L2 caches. SecondLevelDataCache can increase performance by
approximately 2 percent in certain cases for older computers with ample
memory (more than 64 MB) by scattering physical pages better in the
address
space so there are not so many L2 cache collisions. Setting
SecondLevelDataCache to 256 KB rather than 2 MB (when the computer has a
2
MB L2 cache) would probably have about a 0.4 percent performance
penalty.

End quote....

Seems to me that unless you're running a P2 or older that this is a
non-issue.

snip

Setting the SecondLevelDataCache to 2MB??? Thats seems a very high value
to
me?

Either way I am not 100% clued up no the actions of L2 but your post has
helped a little. thought I would share the article as when I checked my
setting on a P4 1.7Ghz there was no value at all.

Regards

Daniel Yates