On Saturday, October 30, 2010 12:24:14 am Brice Goglin wrote:

> Le 30/10/2010 00:01, Jirka Hladky a écrit :

> > On Friday, October 29, 2010 10:59:25 pm Brice Goglin wrote:

> >> Le 29/10/2010 21:57, Jirka Hladky a écrit :

> >>> Hi Samuel,

> >>>

> >>> I have attached the output of

> >>> tests/linux/gather-topology.sh `uname --kernel-release`_`uname --

> >>> nodename`_gather-topology

> >>>

> >>> I'm sorry for the long delay - systems has been used by somebody else,

> >>> I had to wait for it to be free.

> >>>

> >>> System is running kernel 2.6.18-227.el5 (RHEL 5.6). ia64 is not

> >>> supported on RHEL 6.0 so I cannot really test it on the new kernel.

> >>>

> >>> It would be really interesting if you can recognize if it's a kernel

> >>> bug or hwloc problem.

> >>

> >> /sys/devices/system/cpu/cpu*/cache/index4/shared_cpu_map contains an

> >> empty map. This index4 is a L3 cache. But this map means that this cache

> >> is near none of the cores... The instruction L2 has the same problem

> >> (index3 instead of 4). This is a kernel bug.

> >>

> >> But, we already have a dedicated work-around in hwloc

> >>

> >> (src/topology-linux.c):

> >> if (hwloc_bitmap_weight(cacheset) < 1)

> >>

> >> /* mask is wrong (happens on ia64), assumes it's not shared

> >> */ hwloc_bitmap_only(cacheset, i);

> >>

> >> This work-around worked fine on old itaniums since they had one L3, one

> >> L2 and one L1 per core. Your machine has hyperthreading, so our

> >> work-around creates one L3 per thread, while L1 and L2 (properly

> >> reported by the kernel) are core-specific. Maybe hwloc should just

> >> ignore caches with invalid shared_cpu_map.

> >>

> >> Brice

> >>

> >> _______________________________________________

> >> hwloc-devel mailing list

> >> hwloc-devel@open-mpi.org

> >> http://www.open-mpi.org/mailman/listinfo.cgi/hwloc-devel

> >

> > Hi Brice,

> >

> > thanks for looking into it! I'm going to open a BZ for it and put you on

> > the Cc.

>

> Thanks.

Bug 647949 - Wrong /sys/devices/system/cpu/cpu*/cache/index4/shared_cpu_map for L3 and L2 cache on HP Integrity BL870c box with 2 Intel Itanium2 9140N processors

https://bugzilla.redhat.com/show_bug.cgi?id=647949

I put you on Cc.

>

> > BTW, is there some documentation on /sys/devices/system/cpu/* tree?

>

> There's some doc in Documentation/ABI/*/sysfs-devices-* inside the

> kernel source tree.

Thanks!

BTW, it's Intel Itanium2 9140N CPU with 18MB of L3 cache. Kernel reports only 9MB of L3 cache. It's another bug.

Bonne nuit

Jirka