Re: fake cache

Manfred Petz (
Mon, 20 May 1996 21:28:10 +0200 (MET DST)

> > There's this newspaper article about people manufacturing fake cache
> > memory chips, and selling motherboards with these things installed.
> lmbench will show up such machines as diabolically crap performance.
> > It would be nice to have a simple diagnostic to check for this from
> > inside linux.
> Its not simple to test without an Xray machine.

Some time ago, the german computer magazine c't developed a test-program
which unveils such placebo hardware, and it works great.

The program determines the internal & external cache sizes, the type
of cache (write through/back), the cache speed and whether the dirty-tag-RAM
is installed & working or not. This is done with a series of rep stos/movs[bdw]
operations, I guess (I don't have the sources available now, so I can't tell
you exactly).

If the board contains fake caches, the test-program will display a cache size
of zero.

Hmm... Could this be included for /proc/cpuinfo? If yes, I'd take a look at
the source and check whether it's possible to do similar checks at system
startup, ask c't for permission and give it a try. :) Maybe for 2.1.x?