Re: [lhcs-devel] Re: in_atomic doesn't count local_irq_disable?

[Srivatsa Vaddagiri <vatsa@in.ibm.com>]

On Wed, Dec 31, 2003 at 07:05:53PM +0530, Srivatsa Vaddagiri wrote:
> More debugging reveals that the page fault happens
> always while doing a prefetch. The prefetch is
> present inside list_for_each_entry macros.
> 
> For now I have disabled the x86 prefetch function
> to do nothing.
> 
> The test seems to run fine so far w/o any of the 
> page faults I was experiencing. Will update
> at the end of the overnight run if I hit the problem again.
> 
> Wonder if prefetch has some issues on Intel x86 (P3) SMP systems?
> 

Even after disabling prefetch, I continue
to hit page-faults. 

With prefetch disabled, it _always_
traps because of trying to dereference a NULL pointer in a
list-head.  If I break-in into the debugger, the 
list-head is actually valid (no NULL pointer is present) and 
hence I don't understand why it read a NULL pointer value in
a list head.

With prefetch enabled it traps
because of fetch from arbitrary (random) addresses.

So I am no longer sure if this is a prefetch issue
or/and a hotplug issue. I'm continuing to investigate
and will post any new observation I make here.

FYI, the /proc/cpuinfo output on my SMP system is as below:

processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 10
model name      : Pentium III (Cascades)
stepping        : 1
cpu MHz         : 699.730
cache size      : 1024 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse
bogomips        : 1376.25

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 6
model           : 10
model name      : Pentium III (Cascades)
stepping        : 1
cpu MHz         : 699.726
cache size      : 1024 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse
bogomips        : 1396.73


processor       : 2
vendor_id       : GenuineIntel
cpu family      : 6
model           : 10
model name      : Pentium III (Cascades)
stepping        : 1
cpu MHz         : 699.726
cache size      : 1024 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse
bogomips        : 1396.73


processor       : 3
vendor_id       : GenuineIntel
cpu family      : 6
model           : 10
model name      : Pentium III (Cascades)
stepping        : 1
cpu MHz         : 699.726
cache size      : 1024 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 mmx fxsr sse
bogomips        : 1396.73





-- 


Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017