From: c-amb@math.utah.edu (Mark B. Alston) Subject: Re: SUMMARY: Linux performance: WOW! (was: OUCH!) Date: Wed, 30 Jun 1993 22:57:32 GMT
In article <20sq1e$q98@klaava.Helsinki.FI> torvalds@klaava.Helsinki.FI (Linus Torvalds) writes:
d) external cache enabled, 32 MB memory in use:
- the low 16MB is cached externally and internally: very good
- the high 16MB is not cached at all: ten-fold slowdown. Urggh.
result: depending on what pages the process happens to use (directly
and indirectly through buffer cache etc), the program usually works
50% fast mode, 50% slow. Expect 5-6 times slower performance than
with a fully cached system.
Now I really don't know what I am talking about but..
Is is possible to force the system to use the high memory for a ram
drive or for a disk cache? It would seem to me that then the lack of
caching on the memory itself would not be so important. I mean it
still should be faster than a hard drive right?
And on a more specific note... I have 20 MB of memory available. If
I put the 1 MB simms in the first bank and the 4 MB simms in the
second, my bios recongnizes that I have 20 MB of mem available.
However if I flip it around and put the 4 MB simms in the first bank
the second bank isn't found at all. The bios (and linux) report that
I have only 16 MB of mem. So, if the above memory usage is possible,
would it be possible to force the first 4 MB to be a dedicated ram
drive or cache so that I could use all 20 MB? Or in lieu of this
could I make it "hidden" so that linux could use the high 16 MB and
ignore the lower 4 MB? In this way I could use all 20 MB for those
rare visits to dos world.
I have a strange feeling that this all occurs at too low a level for
linux to change anything but it's an idea anyway.
Please let me know if this idea is worth anything or if I am simply
too clueless for words.
Thanks.