Measuring Memory Bandwidth of Non-NT ( Non-Virtual ) memory

[SergeyKostrov]

Hi everybody,

This is an excerpt from a topic'Bypassing Windows NT's Virtual Memory System' which I found on some website:

...
Windows NT includes a boot option, /maxmem, which specifies the maximum amount
of memory NT is allowed to use. This boot option is specified in the c:\\boot.ini
file; for example, the following line limits Windows NT to using 128MB of RAM:

multi(0)disk(0)rdisk(0)partition(1)\\WINNT="Windows NT 4.0 [128]" /maxmem=128

Windows NT will use the first (starting from address 0) 128MB of memory. The
memory above 128MB is available for any driver to utilize. For example, a frame
grabber driver can utilize this Non-NT memory for storing images, without
the 60% DMA space overhead imposed within Windows NT drivers ( frame grabbers
by Matrox and EPIX utilize this ). Developers can also utilize this memory via
the MEMIO example driver given in the Windows DDK. The primary advantage of
using this upper memory instead of user-memory is that it is not virtual, and
thus not swappable ( which provides more deterministic processing of large data
sets ).
...

I've underlined the most interesting parts.

I'm interested to know if somebody has tried to measure a Memory Bandwidth of Non-NT ( Non-Virtual ) memory and has
some performance numbers?

Best regards,
Sergey

[Patrick_F_Intel1]

Hello Sergey,
I don't know of anyone who has experience with bypassing the virtual memory system on windows.
What would like to be able to accomplish?
Have you looked at setting up a ramdisk? Like http://msdn.microsoft.com/en-us/library/windows/hardware/ff544551%28v=vs.85%29.aspxand maybe timing that?
In my opinion, the problem for most folks is that any possible gain in performance is usually offset by the increase in complexity and maintenance cost.
Pat

[SergeyKostrov]

Hi Patrick,

Quoting Patrick Fay (Intel)

...What would like to be able to accomplish?

[SergeyK] There is an idea to use it in a high-performance video processing application.

Have you looked at setting up a ramdisk? Like http://msdn.microsoft.com/en-us/library/windows/hardware/ff544551%28v=vs.85%29.aspxand
maybe timing that?

[SergeyK] I tried thissome time in 2006 and I remember thatRamDisk driver from Microsoft has some limitations
ona size ofRAM-disk ( less than 64MB, or so ). These limitations are related to FAT12 or FAT16.

In my opinion, the problem for most folks is that any possible gain in performance is usually offset by the increase in complexity and maintenance cost.
Pat

Best regards,
Sergey

[Bernard]

Some of the memory is not pageable, for example critical system components like a scheduler,dispatcher and memory manager won't be paged out.Also AWE memory is not pageable. >>>The memory above 128MB is available for any driver to utilize. >>> Could that be a memory which is allocated for the device memory-mapped I/O space and beign used for the other purpose by the dummy(not possesing its own hardware) driver.