Re: utility for testing ram?

Doug Ledford (dledford@dialnet.net)
Thu, 01 Oct 1998 09:04:53 -0500


Stephen C. Tweedie wrote:
>
> Hi,
>
> On Mon, 28 Sep 1998 23:30:18 -0500, Doug Ledford <dledford@dialnet.net>
> said:
>
> >> Start it running overnight, if it's still running when you wake up, your
> >> memory's likely to be ok.
>
> > No, no, and NO! If you want to test your RAM, you can't run some test that
> > is CPU power limited. You'll never access your RAM here faster than the CPU
> > can compile the kernel
>
> Actually, gcc has such a large working set that it turns out to be a
> very good test indeed at least for cache memory. On a 166MHz alpha UDB,
> anything which fits into L1 cache absolutely flies, but kernel compiles
> take about 4 times as long as on my 486-DX100 simply due the the UDB's
> crippled L2 cache size and off-CPU memory bandwidth. Unless you have a
> massive L1 cache like the new 21264s have, gcc speed is quite likely to
> be influenced as much by L2 memory performance as by raw CPU speed.

I'll stand by my claim that my test will trounce a gcc compile test any day
of the week for finding bad RAM %^) The compile test may touch a lot of
RAM, may have a large working set, and may actually compute things fairly
quickly, but gcc can't compile, k for k, as fast as gzip can decompress the
kernel. Then add in the significantly larger amount of data you are running
through RAM in a short period of time via DMA from the disk sub-system and
the compile test won't be able to match the stress the test I listed gives
your machine. I can say this much from experience. Find a machine that
fails my test on one out of every four passes, and I'll show you a machine
that will compile kernels all day long without a hiccup (x86 arch anyway).

-- 

Doug Ledford <dledford@dialnet.net> Opinions expressed are my own, but they should be everybody's.

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