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Reinderien
Asked: 2017-03-19 09:17:20 +0800 CST

Memory clock on DDR2 modules lower than expected

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I've performed a memory upgrade on a Dell Precision T7400. The official user guide states:

Specifications

Memory type: 667- or 800-MHz fully-buffered DDR2 SDRAM fully-buffered DIMMs (FBDs)
Minimum memory: 1 GB
Maximum memory: 64 GB with optional memory riser cards, 32 GB standard

I am not using memory risers. I have 8 x 4GB Samsung 800 MHz FB-DIMM DDR2 (product code M395T5160CZ4-CF76). The memory is working, but at the wrong clock:

$ sudo lshw -C memory | grep FB-DIMM
          description: FB-DIMM DDR2 FB-DIMM Synchronous 667 MHz (1.5 ns)
          description: FB-DIMM DDR2 FB-DIMM Synchronous 667 MHz (1.5 ns)
          description: FB-DIMM DDR2 FB-DIMM Synchronous 667 MHz (1.5 ns)
          description: FB-DIMM DDR2 FB-DIMM Synchronous 667 MHz (1.5 ns)
          description: FB-DIMM DDR2 FB-DIMM Synchronous 667 MHz (1.5 ns)
          description: FB-DIMM DDR2 FB-DIMM Synchronous 667 MHz (1.5 ns)
          description: FB-DIMM DDR2 FB-DIMM Synchronous 667 MHz (1.5 ns)
          description: FB-DIMM DDR2 FB-DIMM Synchronous 667 MHz (1.5 ns)

dmidecode agrees:

$ sudo dmidecode -t memory
# dmidecode 3.0
Getting SMBIOS data from sysfs.
SMBIOS 2.5 present.

Handle 0x1000, DMI type 16, 15 bytes
Physical Memory Array
    Location: System Board Or Motherboard
    Use: System Memory
    Error Correction Type: Multi-bit ECC
    Maximum Capacity: 64 GB
    Error Information Handle: Not Provided
    Number Of Devices: 8

Handle 0x1100, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x1000
    Error Information Handle: No Error
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: FB-DIMM
    Set: None
    Locator: DIMM 1        
    Bank Locator: Not Specified
    Type: DDR2 FB-DIMM
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: 80CE7FB380CE
    Serial Number: 53496E32
    Asset Tag: 010829
    Part Number: M395T5160CZ4-CF76 

Handle 0x1101, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x1000
    Error Information Handle: No Error
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: FB-DIMM
    Set: None
    Locator: DIMM 2        
    Bank Locator: Not Specified
    Type: DDR2 FB-DIMM
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: 80CE7FB380CE
    Serial Number: 052048F7
    Asset Tag: 010812
    Part Number: M395T5160CZ4-CF76 

Handle 0x1102, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x1000
    Error Information Handle: No Error
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: FB-DIMM
    Set: None
    Locator: DIMM 3        
    Bank Locator: Not Specified
    Type: DDR2 FB-DIMM
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: 80CE7FB380CE
    Serial Number: 052048EF
    Asset Tag: 010812
    Part Number: M395T5160CZ4-CF76 

Handle 0x1103, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x1000
    Error Information Handle: No Error
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: FB-DIMM
    Set: None
    Locator: DIMM 4        
    Bank Locator: Not Specified
    Type: DDR2 FB-DIMM
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: 80CE7FB380CE
    Serial Number: 051FD1B0
    Asset Tag: 010811
    Part Number: M395T5160CZ4-CF76 

Handle 0x1104, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x1000
    Error Information Handle: No Error
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: FB-DIMM
    Set: None
    Locator: DIMM 5        
    Bank Locator: Not Specified
    Type: DDR2 FB-DIMM
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: 80CE7FB380CE
    Serial Number: 050BD2E7
    Asset Tag: 010828
    Part Number: M395T5160CZ4-CF76 

Handle 0x1105, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x1000
    Error Information Handle: No Error
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: FB-DIMM
    Set: None
    Locator: DIMM 6        
    Bank Locator: Not Specified
    Type: DDR2 FB-DIMM
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: 80CE7FB380CE
    Serial Number: 060BB367
    Asset Tag: 010828
    Part Number: M395T5160CZ4-CF76 

Handle 0x1106, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x1000
    Error Information Handle: No Error
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: FB-DIMM
    Set: None
    Locator: DIMM 7        
    Bank Locator: Not Specified
    Type: DDR2 FB-DIMM
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: 80CE7FB380CE
    Serial Number: 060BB350
    Asset Tag: 010828
    Part Number: M395T5160CZ4-CF76 

Handle 0x1107, DMI type 17, 27 bytes
Memory Device
    Array Handle: 0x1000
    Error Information Handle: No Error
    Total Width: 72 bits
    Data Width: 64 bits
    Size: 4096 MB
    Form Factor: FB-DIMM
    Set: None
    Locator: DIMM 8        
    Bank Locator: Not Specified
    Type: DDR2 FB-DIMM
    Type Detail: Synchronous
    Speed: 667 MHz
    Manufacturer: 80CE7FB380CE
    Serial Number: 0529DA3A
    Asset Tag: 010825
    Part Number: M395T5160CZ4-CF76

One suspicious message appears in the dmesg MTRR:

[    0.000000] DMI: Dell Inc. Precision WorkStation T7400  /0RW199, BIOS A11 04/30/2012
[    0.000000] e820: update [mem 0x00000000-0x00000fff] usable ==> reserved
[    0.000000] e820: remove [mem 0x000a0000-0x000fffff] usable
[    0.000000] e820: last_pfn = 0x830000 max_arch_pfn = 0x400000000
[    0.000000] MTRR default type: uncachable
[    0.000000] MTRR fixed ranges enabled:
[    0.000000]   00000-9FFFF write-back
[    0.000000]   A0000-BFFFF uncachable
[    0.000000]   C0000-DBFFF write-protect
[    0.000000]   DC000-EFFFF uncachable
[    0.000000]   F0000-FFFFF write-protect
[    0.000000] MTRR variable ranges enabled:
[    0.000000]   0 base 0000000000 mask 2000000000 write-back
[    0.000000]   1 base 00CFF00000 mask 3FFFF00000 uncachable
[    0.000000]   2 base 00D0000000 mask 3FF0000000 uncachable
[    0.000000]   3 base 00E0000000 mask 3FE0000000 uncachable
[    0.000000]   4 base 1FF0000000 mask 3FF0000000 uncachable
[    0.000000]   5 disabled
[    0.000000]   6 disabled
[    0.000000] x86/PAT: Configuration [0-7]: WB  WC  UC- UC  WB  WC  UC- WT  
[    0.000000] total RAM covered: 130047M
... a bunch of gran_size / lose cover RAM ...
[    0.000000] mtrr_cleanup: can not find optimal value
[    0.000000] please specify mtrr_gran_size/mtrr_chunk_size
...
[    0.000000] Memory: 32900928K/33552024K available (8852K kernel code, 1441K rwdata, 3828K rodata, 1556K init, 1296K bss, 651096K reserved, 0K cma-reserved)

Why might my memory be under-clocked, and can I fix this? I do not see any relevant modifiable settings in the BIOS.

memory

1 Answers

  1. Best Answer

    The Dell spec sheet for T7400 says that:

    800MHz memory requires 1600MHz front side bus Xeon processors

    The MTRR part applies to memory layout in Linux, and you should look at fixing that but it has no bearing on memory clock speed.

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