Re: 8.1-PRERELEASE: CPU packages not detected correctly

[David Xu]

Jung-uk Kim wrote:

On Wednesday 14 July 2010 05:40 pm, Jung-uk Kim wrote:

On Wednesday 14 July 2010 01:31 pm, Andriy Gapon wrote:

on 14/07/2010 17:14 Oliver Fromme said the following:

In a machine installed yesterday, 8.1-PRERELEASE doesn't
seem to detect the number of CPU packages vs. cores per

package correctly:
 | FreeBSD 8.1-PRERELEASE-20100713 #0: Tue Jul 13 19:51:18 UTC
 | 2010 [...]
 | CPU: Intel(R) Xeon(R) CPU           L5408  @ 2.13GHz
 | (2133.42-MHz K8-class CPU) Origin = "GenuineIntel"  Id =
 | 0x1067a  Family = 6  Model = 17  Stepping = 10
 | Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,
 |SE
 | P,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,
 |SSE 2,SS,HTT,TM,PBE>
 | Features2=0x40ce3bd<SSE3,DTES64,MON,DS_CPL,VMX,EST,TM2,SSSE3
 |,C X16,xTPR,PDCM,DCA,SSE4.1,XSAVE> AMD
 | Features=0x20000800<SYSCALL,LM>
 |   AMD Features2=0x1<LAHF>
 |   TSC: P-state invariant
 | real memory  = 34359738368 (32768 MB)
 | avail memory = 33151377408 (31615 MB)
 | ACPI APIC Table: <IBM    SERBLADE>
 | FreeBSD/SMP: Multiprocessor System Detected: 8 CPUs
 | FreeBSD/SMP: 1 package(s) x 8 core(s)
 |  cpu0 (BSP): APIC ID:  0
 |  cpu1 (AP): APIC ID:  1
 |  cpu2 (AP): APIC ID:  2
 |  cpu3 (AP): APIC ID:  3
 |  cpu4 (AP): APIC ID:  4
 |  cpu5 (AP): APIC ID:  5
 |  cpu6 (AP): APIC ID:  6
 |  cpu7 (AP): APIC ID:  7
 | ioapic1 <Version 2.0> irqs 24-47 on motherboard
 | ioapic0 <Version 2.0> irqs 0-23 on motherboard

I'm pretty sure that this is a 2 x 4 machine (2 CPU packages
with 4 cores per package), not 1 x 8.  That's what the BIOS
displays during POST.

I'm not sure if this is just a "cosmetic" issue, or if this
is a critical thing ...  I could imagine that performance
might be sub-optimal if the CPU topology isn't detected
correctly, but I'm not sure if FreeBSD can take advantage
of the topology.

Could you please try to do the following?
1. Fetch topo-12212009.tar from the top of this page:
http://software.intel.com/en-us/articles/intel-64-architecture-pr
oc essor-topology-enumeration/ 2. Untar it and apply this patch to
the code:
http://people.freebsd.org/~avg/cpu-topology.diff
3. Compile it by running sh mk_64.sh (supposing you have amd64
system installed) 4. Run cpu_topology64.out and report back its
output.

It's funny that I actually wrote a convenience script (and cleaned
up today):

http://people.freebsd.org/~jkim/cpu_topology-12212009.sh

BTW, current topology detection code is not optimal for some Intel
processors if my memory serves.

Surprisingly, I found a patch I wrote last year from /tmp of my desktop and it is still applied cleanly. 8-)

Just in case, it is available from here:

http://people.freebsd.org/~jkim/mp_machdep.diff

It is applicable to both sys/amd64/amd64/mp_machdep.c and sys/i386/i386/mp_machdep.c. I have to warn you, though, it hasn't been used for more than a year, so it may not work at all. ;-)

Jung-uk Kim

Do you have patch for i386 branch ? I want to test.
On my Pentium-D machine:

$ sysctl kern.sched.topology_spec
kern.sched.topology_spec: <groups>
 <group level="1" cache-level="0">
  <cpu count="2" mask="0x3">0, 1</cpu>
  <flags></flags>
  <children>
   <group level="3" cache-level="2">
    <cpu count="2" mask="0x3">0, 1</cpu>
    <flags></flags>
   </group>
  </children>
 </group>
</groups>

it seems the kernel thinks that the Pentuim-D is sharing L2 cache,
but in fact, the design of the Pentium Ds was simply two P4 cores
sitting side by side. They do not share anything and they basically work
independently.

Regards,
David Xu

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