[coreboot] lower memory performance with coreboot on KGPE-D16

[Daniel Kulesz]

Hi Iru,

> I just found the memory performance on KGPE-D16 is lower when running with
> coreboot. I have two Opteron 6276 and 8 16GB DDR3-1600 RDIMM on all orange
> slots. I tested it with `hdparm -tT /dev/sda` and see the `Timing cached
> reads` result. With coreboot, this value is around 3000 MB/s, but with OEM
> firmware it can go to around 3600 MB/s. I think the disk cached read speed
> is related to memory performance.

Are you using DDR3L-RDIMMs? And did you check whether your memory really runs at 800 MHz? My experience is that coreboot sets the clock down to 667 MHz when running on 1.35V (low voltage), while the vendor bios seems to run modules at 800 MHz in low voltage mode,  resulting in higher performance. According to Timothy, this is  "over the spec" and thus not set in coreboot by default (you can choose between 1.5V 800 MHz or 1.35V at 667 MHz - but may depend on the used modules).

You can check e.g. in dmidecode. Below is an example (serial number x'd out):

Handle 0x000E, DMI type 17, 40 bytes
Memory Device
        Array Handle: 0x0006
        Error Information Handle: Not Provided
        Total Width: 72 bits
        Data Width: 64 bits
        Size: 8192 MB
        Form Factor: DIMM
        Set: None
        Locator: NODE 0 DIMM_D2
        Bank Locator: Not Specified
        Type: DDR3
        Type Detail: Synchronous Registered (Buffered)
        Speed: 800 MHz
        Manufacturer: Samsung
        Serial Number: xxxxxxxxx
        Asset Tag: Not Specified
        Part Number: M393B1K70DH0-YK0  
        Rank: 2
        Configured Clock Speed: 800 MHz
        Minimum Voltage: 1.35 V
        Maximum Voltage: 1.5 V
        Configured Voltage: 1.5 V

Btw.: I am getting around 3700 MB/sec with hdparm -Tt on my /dev/sda (mechanical disk) and around 3840 MB/sec on /dev/nvme0n1 (PCIe M.2 SSD).

Cheers, Daniel