2.4.19-pre2 Cyrix III SEGFAULT (Cyrix II redux?)

2.4.19-pre2 Cyrix III SEGFAULT (Cyrix II redux?)

[S W]

In compiling the kernel, I've been experiencing the
same gcc-2.96 (and gcc-3.0+) SEGFAULT again on Cyrix
III GigaPro (733Mhz, Samuel II core chipset).

But I recalled Linux 2.2 having a bug fix for broken
L2 cache in Cyrix II.  So, it got me thinking again...
(did Cyrix fix this L2 cache in certain subsequential
core?)

Does anyone recall where exactly are the Cyrix II L2
cache bug fix in the kernelso that I can experiement
them toward the Cyrix III?

Assuming no else sees VM bugs, I'll assume that this
is Cyrix-specific.  I've seen various VM BUGs for each
patch releases since 2.4.17 particularly when
compiling.

MOBO DETAILS:
Soyo 7VEM motherboard (686A PL133, despite having an
ALL VIA-chipsets (Cyrix III-733Mhz, VIA-VT82C596A
multifunctional audio/AGPvideo/modem, Rhine Ethernet,
Trident APG), no drivers are loaded into the kernel
except for EXT2, Trident Video (no framebuffer
support) and IDE (via82cxxx.c).  BARE KERNEL.  (BTW,
it was a $250 Fry's special running a barebone
multimedia Linux, so no snickering please.).

Passed memtest86.

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Re: 2.4.19-pre2 Cyrix III SEGFAULT (Cyrix II redux?)

[Dave Jones]

On Sat, Mar 16, 2002 at 10:07:05AM -0800, S W wrote:
 > But I recalled Linux 2.2 having a bug fix for broken
 > L2 cache in Cyrix II.
 
 The cache itself isn't broken. Reporting of the size of it is.
 
 > So, it got me thinking again...
 > (did Cyrix fix this L2 cache in certain subsequential
 > core?)

 The bug is potentially in all cores with cpuid 670->68F
 If you have it, and you're not running a kernel with the
 fix you'll see you have a 16MB cache. If you run a kernel
 with the fix, you'll have the correct size (64KB)
 
 > Does anyone recall where exactly are the Cyrix II L2
 > cache bug fix in the kernelso that I can experiement
 > them toward the Cyrix III?

 arch/i386/kernel/setup.c display_cacheinfo()

-- 
| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

Re: 2.4.19-pre2 Cyrix III SEGFAULT (Cyrix II redux?)

[Alan Cox]

>  > But I recalled Linux 2.2 having a bug fix for broken
>  > L2 cache in Cyrix II.
>  
>  The cache itself isn't broken. Reporting of the size of it is.

He's talking about a different bug. Some early 6x86 processors had weird
problems with cache behaviour that would sometimes break stuff.

Re: 2.4.19-pre2 Cyrix III SEGFAULT (Cyrix II redux?)

[Dave Jones]

On Sat, Mar 16, 2002 at 09:01:06PM +0000, Alan Cox wrote:
 > >  > But I recalled Linux 2.2 having a bug fix for broken
 > >  > L2 cache in Cyrix II.
 > >  The cache itself isn't broken. Reporting of the size of it is.
 > He's talking about a different bug. Some early 6x86 processors had weird
 > problems with cache behaviour that would sometimes break stuff.

 Ah, my bad.  So much errata, so little memory..

-- 
| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

Re: 2.4.19-pre2 CentaurHauls VIA Samuel 2 stepping 2 SEGFAULT (RESOLVED)

[S W]

I pulled the chipset datasheet for CentaurHauls VIA
Samuel 2 stepping 2.

Two seperate i386/kernel/setup.c fixes things seems to
fix this chipset.

1.  Disabled the Branch Predictor in MSR_VIA_FCR
2.  cachesize=0

Other attempts to fix this were:
3.  Disabling L2 Cache OOP'd so that's not an option.
4.  Disables I-Cache (too slow)
5.  Disables D-Cache OOP'd
6.  Disables Page Directory Cache is a NOP.

I've settled for cachesize=0.

Hope this is not a trend here.

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Re: 2.4.19-pre2 CentaurHauls VIA Samuel 2 stepping 2 SEGFAULT (RESOLVED)

[Dave Jones]

On Sat, Mar 16, 2002 at 08:22:41PM -0800, S W wrote:
 > I pulled the chipset datasheet for CentaurHauls VIA
 > Samuel 2 stepping 2.
 > 
 > Two seperate i386/kernel/setup.c fixes things seems to
 > fix this chipset.
 > 
 > 1.  Disabled the Branch Predictor in MSR_VIA_FCR
 > 2.  cachesize=0
 > I've settled for cachesize=0.
 > Hope this is not a trend here.

 Not on the samples I've tested with. I think you have flaky hardware.
 Either there is insufficient cooling/power, or the cache is dead.

-- 
| Dave Jones.        http://www.codemonkey.org.uk
| SuSE Labs

Re: 2.4.19-pre2 Cyrix III SEGFAULT (Cyrix II redux?)

[Alan Cox]

> But I recalled Linux 2.2 having a bug fix for broken
> L2 cache in Cyrix II.  So, it got me thinking again...
> (did Cyrix fix this L2 cache in certain subsequential
> core?)

Certain obscure early 6x86 cpus

> cache bug fix in the kernelso that I can experiement
> them toward the Cyrix III?

The Cyrix III is not even derived from the Cyrix processor line. VIA bought
both Cyrix and IDT's Winchip folks. The Cyrix III is the winchip sequel
(newer versions branded as VIA C3 as VIA dumped the cyrix name completely)

> Assuming no else sees VM bugs, I'll assume that this
> is Cyrix-specific.  I've seen various VM BUGs for each
> patch releases since 2.4.17 particularly when
> compiling.

I suspect hardware problems. A considerable number of people run Cyrix III
C3 and now also Eden systems on Linux. It works very well.

Alan

Re: 2.4.19-pre2 Cyrix III SEGFAULT (Cyrix II redux?)

[Padraig Brady]

We're noticing weirdness here also.
Certain apps are SEGFAULTing. Some apps much
more than others. An important point is that
the apps SEGFAULTed in the exact same place
each time. Doing a trace of the core didn't
show anything weird being executed, it just
SEGFAULTed. Does this suggest a cache issue?
A power cycle changed things (made the faults
more/less frequent). The particular app we were
having trouble with was snmpd (net-snmp). Also
much less frequent was vim and bash. When these
crashed, it was also in the same place. An
important note is that snmpd would crash in
exactly the same place across power cycles.
Recompiling a later version of snmpd "fixed"
the problem. I.E. SEGFAULTs are now very infrequent.
We saved the particular snmpd binary that was
causing trouble, for testing.

We tested with Samuel II & Ezra & Celeron CPUs on
both Advantech PCM9576 & Ibase M700 motherboards.
Celeron was OK, Samuel II was OK, ezra caused segfaults.

We also passed memtest86 (RAM is also ECC) and
multiple kernel compiles worked OK also.

Kernel 2.4.16
gcc version 2.96 20000731 (Red Hat Linux 7.1 2.96-98)
glibc 2.2.4

Padraig.

S W wrote:
> In compiling the kernel, I've been experiencing the
> same gcc-2.96 (and gcc-3.0+) SEGFAULT again on Cyrix
> III GigaPro (733Mhz, Samuel II core chipset).
> 
> But I recalled Linux 2.2 having a bug fix for broken
> L2 cache in Cyrix II.  So, it got me thinking again...
> (did Cyrix fix this L2 cache in certain subsequential
> core?)
> 
> Does anyone recall where exactly are the Cyrix II L2
> cache bug fix in the kernelso that I can experiement
> them toward the Cyrix III?
> 
> Assuming no else sees VM bugs, I'll assume that this
> is Cyrix-specific.  I've seen various VM BUGs for each
> patch releases since 2.4.17 particularly when
> compiling.
> 
> MOBO DETAILS:
> Soyo 7VEM motherboard (686A PL133, despite having an
> ALL VIA-chipsets (Cyrix III-733Mhz, VIA-VT82C596A
> multifunctional audio/AGPvideo/modem, Rhine Ethernet,
> Trident APG), no drivers are loaded into the kernel
> except for EXT2, Trident Video (no framebuffer
> support) and IDE (via82cxxx.c).  BARE KERNEL.  (BTW,
> it was a $250 Fry's special running a barebone
> multimedia Linux, so no snickering please.).
> Passed memtest86.