data corruption with DISABLE_PSE+DISABLE_PG_G: unrelated

[Don Lewis]

On 10 May, Glenn Johnson wrote:
> On Sat, May 10, 2003 at 12:19:51PM -0700, Terry Lambert wrote:
> 
>> Heiko Schaefer wrote:
>>
>> > i'm sorry, my mail was probably a bit confusing. since it has been
>> > pointed out to me, i am running -current kernels with
>> >
>> > options               DISABLE_PSE
>> > options               DISABLE_PG_G
>> >
>> > enabled.
>> >
>> > what i am asking myself:
>> > is there any chance that i still get any data corruption because of
>> > the issues that you write about in some configuration ?!
>>
>> No.  Not with thouse flags set.  If you are getting data corruption
>> with the flags set, then you have some other problem, most likely
>> hardware.

Yup.  Get a copy of memtest86 and run all the tests.  It is actually
pretty good at finding RAM problems.

>> 
>> > because with the 512mb (ddr) ram (which might or might not be
>> > defective) i get data corruption, while with another 256mb (sdr)
>> > ram, i apparently don't.
>> 
>> At Whistle, we had a number of issues with matched simms; the
>> simms from one manufacturer were not good vs. another, supposedly
>> identically rated part.
>>
>> There's also the possibility that the RAM speed is too slow for your
>> FSB speed.  You should be careful here, because not all motherboards
>> are able to detect this mismatch.
> 
> I recently set up 6 AMD AthlonMP-2400+ systems, each with dual
> processors.  I put Corsair memory (256MB) in them which I feel is a
> good brand.  On two of the systems, I had to underclock them to get
> them stable.  They went from 2400+ to 2100+, I forget what the exact
> clock speeds are.  I was getting memory errors at "normal" speed.
> The machines would core dump on certain processes and it was very
> reproducible.  In light of this discussion, I am wondering if I add the
> two kernel options under discussion if I could bring those machines back
> up to their rated speeds and have them be stable.  Any thoughts on that?

Double check the BIOS memory settings.  I've run into motherboards that
set the memory timing incorrectly in the "Auto" mode.  I installed RAM
that was spec'ed as CL 2.5, but the BIOS set the DRAM CAS latency to 2.
I was seeing bits getting flipped when running FreeBSD, and I saw errors
in some of the memtest86 tests.  When I set the memory timing in the
BIOS manually, the errors went away.

> As an adjunct to that, would it be wise to put those options in
> regardless?

I would.  Why configure the system in a way that is known to cause
random errors under wierd and mysterious circumstances?