Author: Robert Hyatt
Date: 13:47:05 11/23/98
Go up one level in this thread
On November 23, 1998 at 15:13:14, Howard Exner wrote: >On November 23, 1998 at 14:05:34, Robert Hyatt wrote: > >>On November 23, 1998 at 10:39:54, Tom Kerrigan wrote: >> >>>On November 23, 1998 at 06:24:34, Alessandro Damiani wrote: >>> >>>>There was a post from Bob Hyatt some days ago. He said the AMD k6 has an error. >>>>If I remember it right it was wrong branching prediction. I don't know if the >>>>error has been eliminated in the k6-2. >>> >>>If the "error" is branch prediction, that just makes the chip slower, but it'll >>>stll do what you want it to... >>> >>>-Tom >> >> >>No.. this error is a killer. If it happens, the chip locks up and not even >>a soft reset will clear it... requires a total power-down. It is similar to >>the "foof" bug for intel, but intel found a quick work-around to fix this. >>AMD hasn't so far. Been a big topic on the linux-SMP mailing list. > >Is this bug you are referring the one from over a year ago? > >This is an article from last year: > >AMD K6 Sprouts Rare Bug > >by Brian McWilliams, PC World NewsRadio > > > September 11, 1997 >Advanced Micro Devices today confirmed that early shipments of its K6 processor >contained a bug that may cause unreliable system behavior in rare situations. > >According to AMD spokesman Dean Whitehair, the bug or erratum only affects K6 >users who are running the Linux operating system on PCs with more than 32MB of >RAM. > >Whitehair says a small number of users have reported encountering system errors >when trying to compile or update Linux on their K6 machines. The erratum does >not impact K6 users on Windows 95 or NT, and Whitehair says it's been fixed in >versions of processor that are shipping now. > >"There're always going to be errata in any processor. Go visit Intel's errata >list, you'll see. And the other thing is we have IBM and Digital using us right >now; they have to go through some very extensive tests that are a lot more >rigorous than many review labs. So we're pretty confident that we have a robust >part." > >Linley Gwennap, editor of the Microprocessor Report, says the K6 Linux bug is in >the same league as Intel's flag erratum that was discovered last May. > >"I would tend to say this was on a similar level; potentially maybe slightly >higher in that nobody really found anyone who was affected by the flag erratum, >whereas in this case clearly some people are affected. But the number is pretty >small and I think that the K6 is certainly safe for the vast majority of >computer users." > >This article sums up my recollection of the AMD bug, as I followed it >on the computer-site newsgroups over a year ago. It was detetected in the early >B series of AMD K6 chips. > >Are Linux users still having problems with the newer K6's (by newer I >mean anything from last summer to the present. Not the B series)? Hard to say whether that is "the bug" or not... because it doesn't say a thing about what it is doing. The bug I saw, reported again by Alan Cox (the person that keeps the 2.0 linux kernel distribution process going) has to do with a branch to a very high address that is a multiple of something like 20000000, that fails. The code he posted was 3 lines of assembly long, and crashed every AMD that it has been run on, to date... At least that was the story on the linux-SMP mailing list. Several reported their machines failed this test, including very recent ones. I don't have an AMD here having run into problems last year with one, so I can't test this myself... But the sources are certainly reliable if you know Alan and the other "kernel hackers"...
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