From: pyeatt@Texaco.com (Larry D. Pyeatt) Subject: Re: SUMMARY: Linux performance: WOW! (was: OUCH!) Date: Wed, 30 Jun 1993 14:04:38 GMT
In article <C9EG6o.7En@inviso.com>, gilbert@inviso.com (Gilbert Callaghan) writes:
|> Anyway, most people suggested that I try, as a test, a kernel compiled
|> to use only up to 16 Meg. Then I re-tried my compile test: 2:48.1
|>
|> Yes! Just a tad slower than ISC; that's ok.
|>
|> Or so I thought - then it got even better. I went into my CMOS and found
|> that the cache was completely DISABLED! SO I enabled it (128k cache) and
|> ran my compile test in 1:47.0 minutes! Far better than ISC can do.
|>
|> Naturally I started wondering if the cache was enabled on the ISC box.
|> So I took it down and found that it WAS.
|>
|> One last test. Since caching is now enabled, I re-tried it with the
|> 32Meg kernel. I got a very slow 6:34.0 result.
|>
|> Personally, I'm happy now. I can run at blazing speed with 16 Meg, which
|> is enough for me. There does still seem to be a problem, though. It
|> appears that this has nothing to do with caching, as caching speeds up
|> both the 16M and the 32M kernels. And I have received mail from other
|> people who are experiencing the same thing. Hopefully we can unravel
|> this mystery soon.
|>
|> Perhaps it's a motherboard problem; I'm not sure.
Almost certainly a cache problem.
I have seen this sort of behavior several times before. The most
common explaination is "cache tag ram." For some stupid reason,
most motherboards come with enough cache tag ram so that they can
cache the first 16M, but not the second 16M. So, even with the cache
enabled, and 256K of cache installed, it can only cache the lower 16M.
So, when your program is using the upper memory, it gets real slow, but
not quite as slow as no cache at all. Most boards allow you to install
an additional tag ram chip.
I just noticed you said 128K cache. You may need to expand that to
256K, and you maym or may not need additional cache tag ram.
--
Larry D. Pyeatt This article does not reflect the views
( pronounced "Johnson" ) of my employer or of myself. Any simi-
Internet : pyeatt@texaco.com larity to the views of anyone, real or
Voice : (713) 975-4056 fictional, is purely coincidental.