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Date:	Wed, 24 Dec 2014 23:08:18 +0100
From:	Pavel Machek <>
To:	Mark Seaborn <>,
	kernel list <>
Subject: Re: DRAM unreliable under specific access patern


> Try this test program:
> It has reproduced bit flips on various machines.
> Your program won't be an effective test because you're just hammering
> addresses x and x+64, which will typically be in the same row of

Yep, I found out I was wrong in the meantime.

> For the test to be effective, you have to pick addresses that are in
> different rows but in the same bank.  A good way of doing that is just to
> pick random pairs of addresses (as the test program above does).  If the
> machine has 16 banks of DRAM (as many of the machines I've tested on do),
> there will be a 1/16 chance that the two addresses are in the same
> bank.

How long does it normally teake to reproduce something on the bad machine? 

> [Replying off-list just because I'm not subscribed to lkml and only saw
> this thread via the web, but feel free to reply on the list. :-) ]

Will do. (Actually, it is ok to reply to lkml even if you are not
subscribed; lkml is open list.).

In the meantime, I created test that actually uses physical memory,
8MB apart, as described in some footnote. It is attached. It should
work, but it needs boot with specific config options and specific
kernel parameters.

[Unfortunately, I don't have new-enough machine handy].

Best regards,
(cesky, pictures)

View attachment "disturb.c" of type "text/x-csrc" (1847 bytes)

View attachment "disturb.c" of type "text/x-csrc" (1848 bytes)

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