Hi Jon,
On Sun, Apr 25, 2010 at 01:21:04PM -0400, Jon Stanley wrote:
> When trying to discover the NUMA topology of a system in a script, for
> example. lscpu -p seems the perfect format to do so. However, it's not
> accurate, because the CPU identifiers given in the first column bear
> no relation whatsoever to the actual CPU's as seen by the OS. Take
> this from an IBM x440 (I think) running RHEL5.4 (which is a 2x4-core
> Nehalem):
Let's hope that this old kernel has
/sys/devices/system/cpu/*
/sys/devices/system/node/*/cpumap
directories :-)
> [jstanley@xen06 ~]$ ./lscpu -p
> # The following is the parsable format, which can be fed to other
> # programs. Each different item in every column has an unique ID
> # starting from zero.
> # CPU,Core,Socket,Node,,L1d,L1i,L2,L3
> 0,0,0,0,,0,0,0,0
> 1,1,0,0,,1,1,1,0
> 2,2,0,0,,2,2,2,0
> 3,3,0,0,,3,3,3,0
> 4,4,1,1,,4,4,4,1
> 5,5,1,1,,5,5,5,1
> 6,6,1,1,,6,6,6,1
> 7,7,1,1,,7,7,7,1
>
> CPU's 0-3 might not be on node0 (though in this particular system,
> they happen to be - I was trying to find a non-work system exhibiting
> the problem and failed :) ). At any rate, on an Opteron at work, the
> output looks very similar, but node 0 consists of CPU's 0 and 2, not 0
> and 1. It gets worse when you get into higher-core systems.
>
> I looked into the source code, and it appears that lscpu actually
> throws away all of the NUMA topology information that it gets. If I
> read the source code correctly, then it counts the number of nodes,
> cores, and sockets by looking only at cpu0, and simply says "OK,
> there's 4 cores/socket here, let's call them 0-3 and 4-7, regardless
> of what the OS thinks they are". Not entirely useful.
>
> My C-fu is much too weak to attempt to patch this, but I can provide
> testing if needed :)..
The lscpu(1) could be executed against a different /{proc,sys} directory,
for example:
lscpu --sysroot /ibm-x440
It allows to debug lscpu outside the original machine.
Please, use tests/ts/lscpu/mk-input.sh script (from util-linux-ng
tarball or git tree or
http://git.kernel.org/?p=utils/util-linux-ng/util-linux-ng.git;a=blob_plain;f=tests/ts/lscpu/mk-input.sh;hb=HEAD
) and make a copy of your /{proc,sys} by:
mk-input.sh ibm-x440
it will generate ibm-x440.tar.gz. Please, send me this tarball.
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
--
To unsubscribe from this list: send the line "unsubscribe util-linux-ng" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
