[eigen] cache queries bug?

[Ben Goodrich <bgokgm@xxxxxxxxxxxxxx>]

Hi,

If you want to postpone this until after the beta is released, that is fine.

I have two machines, both with the "same" software (disregarding the
bitness difference) with Debian unstable and g++ 4.4.4.

One is a core duo desktop from a couple of years ago

bgoodrich@Room320:/tmp/eigen/test$ cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 15
model name      : Intel(R) Core(TM)2 CPU          6300  @ 1.86GHz
stepping        : 6
cpu MHz         : 600.000
cache size      : 2048 KB
physical id     : 0
siblings        : 2
core id         : 0
cpu cores       : 2
apicid          : 0
initial apicid  : 0
fpu             : yes
fpu_exception   : yes
cpuid level     : 10
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe
syscall nx lm constant_tsc arch_perfmon pebs bts rep_good aperfmperf
pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm
tpr_shadow
bogomips        : 3721.67
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

processor       : 1
vendor_id       : GenuineIntel
cpu family      : 6
model           : 15
model name      : Intel(R) Core(TM)2 CPU          6300  @ 1.86GHz
stepping        : 6
cpu MHz         : 600.000
cache size      : 2048 KB
physical id     : 0
siblings        : 2
core id         : 1
cpu cores       : 2
apicid          : 1
initial apicid  : 1
fpu             : yes
fpu_exception   : yes
cpuid level     : 10
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge
mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe
syscall nx lm constant_tsc arch_perfmon pebs bts rep_good aperfmperf
pni dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm lahf_lm
tpr_shadow
bogomips        : 3720.69
clflush size    : 64
cache_alignment : 64
address sizes   : 36 bits physical, 48 bits virtual
power management:

and one is a really old laptop (don't laugh)

goodrich@X41Laptop:/tmp/eigen$ cat /proc/cpuinfo
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 13
model name      : Intel(R) Pentium(R) M processor 1.50GHz
stepping        : 8
cpu MHz         : 600.000
cache size      : 2048 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 clflush dts acpi mmx fxsr sse sse2 ss tm pbe nx up bts est
tm2
bogomips        : 1196.71
clflush size    : 64
cache_alignment : 64
address sizes   : 32 bits physical, 32 bits virtual
power management:

On the 32 bit laptop, I have encountered a problem where things like

../check.sh cholesky

hang for minutes before I kill them, while on the 64 bit core duo
desktop, this finishes in a few seconds.

I bisected the problem to

goodrich@X41Laptop:/tmp/eigen$ hg bisect --bad
The first bad revision is:
changeset:   3027:c93abfa8ffcb
parent:      3023:c3b8e6edde53
user:        Gael Guennebaud <g.gael@xxxxxxx>
date:        Wed Jun 23 16:34:51 2010 +0200
summary:     fix cache queries for non core2 CPU ;)

But I don't know what to do from here because I don't really
understand low-level issues like this.

Thank you,
Ben