Hi,
Sorry to have bothered you all but there is no degradation of
performance with hpl and kernel upto 2.6.25-rc6. It was my silly error!
The motherboards I use are two Asus p5e vm do and 3 ASus p5k-vm with
intel Q6600 quad cpus with GO stepping oveclocking them slightly i now
get 165 GFlops for my 5 node quad core cluster
with gotoblas v1.24 and hpl and opensource openmpi v 1.3 alpha.
My error was that the CPUID LIMIT was enabled in bios which is for older
windows systems which prevents the cpuid instruction on boot up from
filling the register EAX with values above 0x03
So I was seeing only 2 cores for a quad core in cat /proc/cpuinfo on all
nodes giving me lousy performance for every kernel except some like
2.6.23.13 and 2.6.23.14.since i was oversubscribibg each node with 4
processes and top -H confirmed that.
Now I disabled CPUID LIMIT for each node and i see alll 4 processors on
eac node with cat /proc/cpuinfo for kernel ver 2.6.25-rc6 and i get
38.44 -38.9 Gflops per node. Ofcourse i am stably overclocking each
q6600 by approx 480mhz to get that otherwise for the kentsfiel q6600
intel at 2.4 GHZ the peak is 38.4 GFlops( reference paper by Dr. Jack
Dongarra et al.)
The bios message is misleading : It says " Disable for Windows Xp" and
since I am running linux I enable it till i Googled for CPUID LIMIT and
found out and experimented!
So for your info disable CPUID LIMIT in bios when running quad core
linux or more! It's meant for old oses like win98 etc.
Thank you and and sorry for the bother it was my error and not a fault
in the kernels. This is FYI only.
Cheers,
Allan Menezes
Allan Menezes <[email protected]> writes:
> from filling the register EAX with values above 0x03
> So I was seeing only 2 cores for a quad core in cat /proc/cpuinfo on
> all nodes giving me lousy performance for every kernel except some
> like 2.6.23.13 and 2.6.23.14.
You say some older kernels behaved better than newer ones in the two
core oversub configuration? That would be still an issue that should
be investigated. After all Linux should run well even with
oversubscribing on two cores.
-Andi