Memory XMP profile seems to make CPU slow down

ErikRedbeard · February 22, 2020

Having issues with a Haswell cpu in combination with a 2x16GB kit's memory profile on a friends pc.

Motherboard: Gigabyte GA-X99-UD3 (rev. 1.0)
Bios: F23c

Memory: G.Skill F4-3000C16D-32GISB
CPU : Intel i7 5820K

With XMP disabled the CPU runs and boosts fine and it can utilise to 100%

2100 15-15-15-36
But when I turn on XMP (only 1 profile) the cpu stops going over 2.9Ghz and running Cinebench R20 or Prime95 the utilisation doesn't go over 90%.

Picture from running CinebenchR20
PS: I did actually notice it said 3751Mhz CPU clock on MSI Afterburners monitor now that I'm looking at the pictures while inserting them.

We've tried setting the frequency, timings and voltage of the XMP profile manually, but that resulted in not booting at all.

3000 16-18-18-38 1.35v

We've tried setting it to

2600 16-18-18-38 1.35v

After that we noticed that the XMP profile (only 1 profile available) sets the Processor Base Clock Multiplier to 1.25 (125Mhz) instead of the default 100Mhz.
Manually lowering this to 1.0.
Which resulted in the memory frequency going down to 2400Mhz since that's the base multiplier.

Currently we're just running the system without XMP or any manual overclock.
But to me it's very weird an XMP profile would up the base clock by that much and in turn having utilisation issues.

Picture of default values with XMP enabled.

I'm confused on what is happening here. So here are my main questions at this moment:

Is taskmanager just by default basing everything on a 100Mhz BCLK? And would that also explain the 90% utilisation.?

Am I correct in the assumption that it actually all works fine with XMP enabled and taskmanager just gives wrong information here?

-And if so is there something one can do to change the BCLK for taskmanager?

-If not what can we do to actually get a higher speed than 2133

Jurrunio · February 22, 2020

Read CPU frequency with software like CPU-Z or better, Hwinfo. From what I can observe with my 2600k system Windows Task Manager always treats BCLK as 100MHz, but this doesnt seem to always be the case.

125MHz thing is called a BCLK strap because back in X99 days, CPUs dont respond well to memory overclock through multiplier and raising BCLK is the best way to make higher frequencies run.

ErikRedbeard · February 23, 2020

21 hours ago, Jurrunio said:

Read CPU frequency with software like CPU-Z or better, Hwinfo. From what I can observe with my 2600k system Windows Task Manager always treats BCLK as 100MHz, but this doesnt seem to always be the case.

125MHz thing is called a BCLK strap because back in X99 days, CPUs dont respond well to memory overclock through multiplier and raising BCLK is the best way to make higher frequencies run.

HWinfo does indeed show the correct values.

Thank you for the help in clarifying what we were seeing.