[Linux-aus] HT Xeon and Linux Kernel (was Re:)

Fri Jan 30 13:45:02 UTC 2004

On 30/01/2004, at 2:57 PM, Leigh Dyer wrote:

> On Fri, 2004-01-30 at 12:52, Anshul Gupta wrote:
>> Hi All,
>>
>> I have upgraded the kernel from 2.4.20-28.9 to 2.4.24 on a 4-processor
>> machine and somehow only 2 processors are detected now.  All 4
>> processors were detected in 2.4.20-28.9.
>>
>
> Does the machine really have four physical CPUs? AFAIK, all P4 Xeon 
> CPUs
> support hyperthreading, which makes each physical CPU look like two
> seperate CPUs when enabled. This counfused the crap out of me before 
> the
> penny dropped when I got my hands on a couple of dual-Xeon servers 
> (dual
> 2.8Ghz chips in one, dual 2.4s in the other), since while I knew each
> machine only had two CPUs, /proc/cpuinfo and dmesg showed 4.
>

  Checked the specs of the machine, It has 2 processors actually. :-)

> Earlier 2.4 kernels reported each virtual CPU seperately, which is why
> my dual machines looked like they had four CPUs. Later versions are
> hyperthreading-aware, and report only the number of physical CPUs. I'm
> not sure when that change was made, but it's possible that it was
> somewhere between your two kernel versions.
>

I am running 2.4.24 but if it's hyperthreading aware why it now detects 
4 CPU when I have increased CONFIG_NR_CPUS from 4 to 8!!

Here's a extract from the output of dmesg.

-----------OUTPUT WITH 4 PROCESSORS-------------
ACPI: LAPIC (acpi_id[0x01] lapic_id[0x00] enabled)
Processor #0 Pentium 4(tm) XEON(tm) APIC version 20
ACPI: LAPIC (acpi_id[0x02] lapic_id[0x06] enabled)
Processor #6 Pentium 4(tm) XEON(tm) APIC version 20
ACPI: LAPIC (acpi_id[0x03] lapic_id[0x01] enabled)
Processor #1 Pentium 4(tm) XEON(tm) APIC version 20
ACPI: LAPIC (acpi_id[0x04] lapic_id[0x07] enabled)
Processor #7 Pentium 4(tm) XEON(tm) APIC version 20
Using ACPI for processor (LAPIC) configuration information
Intel MultiProcessor Specification v1.1
     Virtual Wire compatibility mode.
OEM ID: INTEL    Product ID: SPRINGDALE_G APIC at: 0xFEE00000
I/O APIC #8 Version 32 at 0xFEC00000.
Enabling APIC mode: Flat.       Using 1 I/O APICs
Processors: 4
Kernel command line: ro root=LABEL=/
Initializing CPU#0
Detected 2400.133 MHz processor.
Console: colour VGA+ 80x25
Calibrating delay loop... 4784.12 BogoMIPS
Memory: 1032712k/1048512k available (1838k kernel code, 15412k 
reserved, 641k data, 140k init, 131008k highmem)
Dentry cache hash table entries: 131072 (order: 8, 1048576 bytes)
Inode cache hash table entries: 65536 (order: 7, 524288 bytes)
Mount cache hash table entries: 512 (order: 0, 4096 bytes)
Buffer cache hash table entries: 65536 (order: 6, 262144 bytes)
Page-cache hash table entries: 262144 (order: 8, 1048576 bytes)
CPU: Trace cache: 12K uops, L1 D cache: 8K
CPU: L2 cache: 512K
CPU: Physical Processor ID: 0
Intel machine check architecture supported.
Intel machine check reporting enabled on CPU#0.
CPU:     After generic, caps: bfebfbff 00000000 00000000 00000000
CPU:             Common caps: bfebfbff 00000000 00000000 00000000
Enabling fast FPU save and restore... done.
Enabling unmasked SIMD FPU exception support... done.
Checking 'hlt' instruction... OK.
POSIX conformance testing by UNIFIX
mtrr: v1.40 (20010327) Richard Gooch (rgooch at atnf.csiro.au)
mtrr: detected mtrr type: Intel
CPU: Trace cache: 12K uops, L1 D cache: 8K
CPU: L2 cache: 512K
CPU: Physical Processor ID: 0
Intel machine check reporting enabled on CPU#0.
CPU:     After generic, caps: bfebfbff 00000000 00000000 00000000
CPU:             Common caps: bfebfbff 00000000 00000000 00000000
CPU0: Intel(R) Xeon(TM) CPU 2.40GHz stepping 07
per-CPU timeslice cutoff: 1462.38 usecs.
enabled ExtINT on CPU#0
ESR value before enabling vector: 00000000
ESR value after enabling vector: 00000000
Booting processor 1/1 eip 2000
Initializing CPU#1
masked ExtINT on CPU#1
ESR value before enabling vector: 00000000
ESR value after enabling vector: 00000000
Calibrating delay loop... 4797.23 BogoMIPS
CPU: Trace cache: 12K uops, L1 D cache: 8K
CPU: L2 cache: 512K
CPU: Physical Processor ID: 0
Intel machine check reporting enabled on CPU#1.
CPU:     After generic, caps: bfebfbff 00000000 00000000 00000000
CPU:             Common caps: bfebfbff 00000000 00000000 00000000
CPU1: Intel(R) Xeon(TM) CPU 2.40GHz stepping 07
Booting processor 2/6 eip 2000
Initializing CPU#2
masked ExtINT on CPU#2
ESR value before enabling vector: 00000000
ESR value after enabling vector: 00000000
Calibrating delay loop... 4797.23 BogoMIPS
CPU: Trace cache: 12K uops, L1 D cache: 8K
CPU: L2 cache: 512K
CPU: Physical Processor ID: 3
Intel machine check reporting enabled on CPU#2.
CPU:     After generic, caps: bfebfbff 00000000 00000000 00000000
CPU:             Common caps: bfebfbff 00000000 00000000 00000000
CPU2: Intel(R) Xeon(TM) CPU 2.40GHz stepping 09
Booting processor 3/7 eip 2000
Initializing CPU#3
masked ExtINT on CPU#3
ESR value before enabling vector: 00000000
ESR value after enabling vector: 00000000
Calibrating delay loop... 4797.23 BogoMIPS
CPU: Trace cache: 12K uops, L1 D cache: 8K
CPU: L2 cache: 512K
CPU: Physical Processor ID: 3
Intel machine check reporting enabled on CPU#3.
CPU:     After generic, caps: bfebfbff 00000000 00000000 00000000
CPU:             Common caps: bfebfbff 00000000 00000000 00000000
CPU3: Intel(R) Xeon(TM) CPU 2.40GHz stepping 09
Total of 4 processors activated (19175.83 BogoMIPS).
cpu_sibling_map[0] = 1
cpu_sibling_map[1] = 0
cpu_sibling_map[2] = 3
cpu_sibling_map[3] = 2
--------------------END-----------------------------------

There is something wrong.

Cheers,
Anshul