Date: Thu, 24 Nov 2005 20:26:05 +0100
From: Andi Kleen <ak@suse.de>
To: thockin@hockin.org
Cc: "Eric W. Biederman" <ebiederm@xmission.com>, Andi Kleen <ak@suse.de>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, Gerd Knorr <kraxel@suse.de>,
       Linus Torvalds <torvalds@osdl.org>, Dave Jones <davej@redhat.com>,
       Zachary Amsden <zach@vmware.com>, Pavel Machek <pavel@ucw.cz>,
       Andrew Morton <akpm@osdl.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       "H. Peter Anvin" <hpa@zytor.com>,
       Zwane Mwaikambo <zwane@arm.linux.org.uk>,
       Pratap Subrahmanyam <pratap@vmware.com>,
       Christopher Li <chrisl@vmware.com>, Ingo Molnar <mingo@elte.hu>
Subject: Re: [patch] SMP alternatives
Message-ID: <20051124192604.GS20775@brahms.suse.de>
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On Thu, Nov 24, 2005 at 11:16:36AM -0800, thockin@hockin.org wrote:
> On Thu, Nov 24, 2005 at 06:58:52AM -0700, Eric W. Biederman wrote:
> > > That's supposed to be done by hardware, no? 
> > > At least the K8 has a hardware scrubber (although it's not always enabled)
> > 
> > Recent good implementations like the Opteron will do it for you.
> > Older or cheaper memory controllers will not.
> 
> Beware of errata - there's at leats one errata on Opteron which forces you
> to choose between x4 (chipkill) ECC and scrubber.  One or the other, but
> not both.  There are plenty of errata on the scrubber alone.  Worse, if my
> (brain)memory is correct, without the scrubber, correctable errors are
> corrected on the fly, but never written back to DRAM.

All the scrub errata were fixed with E stepping AFAIK.

You have a point that using a sw scrubber might make sense on earlier
steppings though in case someone really wants chipkill.

-Andi
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