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"CPU Load-line Calibration" vs "SVID Behavior" vs "IA AC/DC Load Line" settings

Snafu42
Level 9

At least 3 BIOS settings affect the mOhm values reported by HWINFO as "IA Domain Loadline (AC/DC)". BIOS should IMO also report these values but does not. Here some test results for the ROG STRIX Z790-E Gaming Wifi BIOS 2503:

DIGI+ VRM\CPU Load-line Calibration:

Auto: 0.45 / 1.10 mOhm ("Current CPU Load-line Calibration: LEVEL 3")
1:    1.70 / 1.70 mOhm
2:    1.46 / 1.46 mOhm
3:    1.10 / 1.10 mOhm (DC_LL/AC_LL max values from Intel Datasheet)
4:    1.00 / 1.00 mOhm ("4: Recommended for OC", F5 default)
5:    0.73 / 0.73 mOhm
6:    0.49 / 0.49 mOhm
7:    0.24 / 0.24 mOhm
8:    0.01 / 0.01 mOhm

(BTW: "Auto" is set by the "Enable AI" button of "AI OC Guide" but not by EZ-Mode "AI Overclocking" switch, see topic AI Overclocking quick settings do different things)

The above may be partly or fully overridden by this setting ("----": no change):

SVID Behavior:

Auto:                ---- / ---- mOhm (F5 default)
Best-Case Scenario:  0.01 / ---- mOhm
Typical Scenario:    0.40 / ---- mOhm
Worst-Case Scenario: 0.60 / ---- mOhm
Intel's Fail Safe:   1.10 / 1.10 mOhm

This again may be overridden by:

Internal CPU Power Management\IA AC Load Line
Internal CPU Power Management\IA DC Load Line

Questions:
1. Does it make sense to set AC LL and DC LL to very different values as "CPU LLC: Auto" does?

2. The following two sets of settings result in same AC/DC LL mOhm values. What is the behavioral difference, if any?

CPU Load-line Calibration: 6
SVID Behavior: Auto
IA AC Load Line: Auto
IA DC Load Line: Auto

CPU Load-line Calibration: 4
SVID Behavior: Auto
IA AC Load Line: 0.49
IA DC Load Line: 0.49

3. The same question applies to this example:

CPU Load-line Calibration: 6
SVID Behavior: Typical Scenario
IA AC Load Line: Auto
IA DC Load Line: Auto

CPU Load-line Calibration: 4
SVID Behavior: Auto
IA AC Load Line: 0.40
IA DC Load Line: 0.49

 

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Snafu42
Level 9

Another setting which affects "IA Domain Loadline (AC/DC)":

DIGI+ VRM\Sync ACDC Loadline with VRM Loadline

It is Enabled by default. If set to Disabled, the AC LL is apparently always set to the Auto value such that the above table for CPU Load-line Calibration changes to:

Auto: 0.45 / 1.10 mOhm
1:    0.45 / 1.70 mOhm
...
8:    0.45 / 0.01 mOhm

This again may be overriden by SVID Behavior etc.

The naming "Sync ACDC Loadline..." is misleading. If set to Disabled, it apparently only affects IA AC LL. IA DC LL is still synced with the LLC level.

In which situations does it make sense to set this setting to Disabled?

Hi @Snafu42 I am also trying to learn how various configuration values interact and what is the right configuration so thank you for starting this post.

According to Testing and Optimizing the 0x129 Microcode on the ASUS Maximus Z790 Apex Encore YouTube video of BUILDZOID at https://www.youtube.com/watch?v=XI2x2_skwSs some of things you have mentioned above are also mentioned and he goes through his thoughts around what is going on with these BIOS settings. In this video he shares how to keep the CPU cool yet performant as long as you are on Microcode 129 which he also explains why that is needed.

I have watched this video couple of times to get a better understanding and so far I have understood the following which could still be flawed or incorrect.

  • The load lines help to undervolt the CPU as they reduce the requested CPU voltage (VID).
  • Enabling TVB also reduces the requested voltage by a small value. he mentions 50 mVolts.
  • Finally any unvervolting via Global Core SVID Voltage using the Adaptive mode will apply a range of undervolting depending upon the CPU frequency i.e. it is not a fixed voltage reduction like the above two points.

There is a detailed video he did called ABSOLUTELY EVERYTHING ABOUT LOAD LINES ON LGA1700 // why intel needed to add a 1.55V VID limit which can be viewed at https://www.youtube.com/watch?v=9slwXKUwmnE where he explains a lot more about Load Lines and how they are affecting / reducing the requested CPU voltage (VID) as well.

I am still trying to parse all this information properly. Hope this helps you out and maybe you can share your understanding as well.

 

Disclaimer: I am not an ASUS support person so my information may be incomplete. Always follow official documentation and material provided by ASUS representatives.

INTEL i9-14900K / CORSAIR VENGEANCE RGB 192GB (4x48GB) 5200 CAS38 / ROG Z790 DARK HERO / ROG TUF GAMING RTX 4090 OC / ProArt PA-602 Case / SEASONIC PRIME TX-1300 ATX 3.0 / CORSAIR MP700 PRO 2TB PCIe Gen5 / CRUCIAL T500 2TB PCIe Gen4 / EIZO CG2700X
TL;DW: BIOS 1503 with the 0x129 Microcode successfully limits max Vcore to 1.55V when using the intel default settings. My Patreon: https://www.patreon.com/buildzoid Teespring: https://teespring.com/stores/actually-hardcore-overclocking Bandcamp: https://machineforscreams.bandcamp.com/music My ...
My Patreon: https://www.patreon.com/buildzoid Teespring: https://teespring.com/stores/actually-hardcore-overclocking Bandcamp: https://machineforscreams.bandcamp.com/music My game: https://buildzoid.itch.io/hv-shooter Twitch: https://www.twitch.tv/buildzoid Twitter: https://twitter.com/Buildzoid1

Hipflask
Level 10

 "The following two sets of settings result in same AC/DC LL mOhm values. What is the behavioral difference, if any?"

I'm assuming the reason you're asking this is because there's no noticeable difference when reading the die sense voltage measurement via software. In which case, you'd need the necessary measurement equipment in order to see the transients (if there were any different at all).

My understanding is that manually setting the IA AC DC Load Line Values overrides the Load Line Calibration Level value. Since you are manually setting the load line value of a LEVEL 6 hence everything is measuring to be the same even though you selected the LEVEL 4 as the baseline (sometimes also referred to as preset).

The Level values are considered to be presets provided by ASUS BIOS. If you do not like these preset values (which simply shortcuts) then you can manually set any value for your overclocking needs based on your system build since every system build is unique and different due to silicon lottery and motherboard variance etc.

Disclaimer: I am not an ASUS support person so my information may be incomplete. Always follow official documentation and material provided by ASUS representatives.

INTEL i9-14900K / CORSAIR VENGEANCE RGB 192GB (4x48GB) 5200 CAS38 / ROG Z790 DARK HERO / ROG TUF GAMING RTX 4090 OC / ProArt PA-602 Case / SEASONIC PRIME TX-1300 ATX 3.0 / CORSAIR MP700 PRO 2TB PCIe Gen5 / CRUCIAL T500 2TB PCIe Gen4 / EIZO CG2700X

I wish to know either for ac/dc load lines LLC levels and how it relates to svid behavior if I understand correctly  

the more the LLC higher the less voltage on idle but more voltage under load? Or the opposite ?

intel Core i9 14900KS SP108 MC SP95 P-Cores SP122 E-Cores SP81 | ASUS ROG Maximus Z790 Apex Encore (BIOS 1703) | 2X24GB G.Skill RAM 8600MHZ CL38 OC/Tuned | Nvidia RTX 4080 ROG STRIX

"the more the LLC higher the less voltage on idle but more voltage under load? Or the opposite ?"

Lower LLC level: Higher idle voltage, higher drop under load, lower under/overshoot.
Higher LLC level: Lower idle voltage, lower drop under load, higher over/undershoot.

See: https://elmorlabs.com/2019-09-05/vrm-load-line-visualized/

The "Prediction" section in the right BIOS column may give some hint. It is updated a few seconds after changing the LLC level. On my system, the predicted voltages drop by 0.019-0.022V with each increase of LLC level between 1 and 6. There is no change between 6 and 8.

 

So if I’m on svid behavior best case scenario and LLC6 it’s fine? Should I stay like that? Or try LLC6?

intel Core i9 14900KS SP108 MC SP95 P-Cores SP122 E-Cores SP81 | ASUS ROG Maximus Z790 Apex Encore (BIOS 1703) | 2X24GB G.Skill RAM 8600MHZ CL38 OC/Tuned | Nvidia RTX 4080 ROG STRIX

What about the setting Synch ac/dc loadline with vrm should I keep it enabled ? By default it enabled for me apex encore and as for IA cep right now I’m enabled should I keep it like that with best case scenario which is kind of undervolt right?

intel Core i9 14900KS SP108 MC SP95 P-Cores SP122 E-Cores SP81 | ASUS ROG Maximus Z790 Apex Encore (BIOS 1703) | 2X24GB G.Skill RAM 8600MHZ CL38 OC/Tuned | Nvidia RTX 4080 ROG STRIX

"What about the setting Synch ac/dc loadline with vrm should I keep it enabled ?"

According to the (by HWINFO) observed behavior on my system, Sync ACDC Loadline with VRM Loadline has no effect if SVID Behavior is not Auto.

"... should I keep it like that with best case scenario which is kind of undervolt right?

SVID Behavior: Best-Case Scenario sets a minimal AC_LL of 0.01 mOhm. AFIAK this results in minimal possible (e.g. +0.002V at 200A) additional VID under load (VID = Base_VID + AC_LL*Current). This should provide undervolting (mostly) under load.

The DC_LL is not affected by Best-Case Scenario. It is still set by the CPU LLC level (e.g. 0.490 mOhm for level 6) if not overridden later by the direct settings. IIRC Intel recommends AC_LL = DC_LL which is not the case here. This leads back to my question 1 from the original post.

A possibly interesting setting is SVID Behavior: Trained which is also mentioned on the AI Features BIOS page. It results in AC_LL of 0.14 mOhm on my system. Possibly a more reasonable value than the extreme 0.01 from Best-Scenario. The name Trained may suggests that the value could change over time, Hmm...

I currently use CPU LLC: 6 (results in AC_LL=DC_LL=0.490 mOhm), Global Core SVID Voltage: Adaptive -0.10 and IA VR Voltage Limit: 1450. It runs stable, at least without OC. Max Vcore and VID do not exceed 1.35V during stress tests. I'm aware that Vcore measurement may be less accurate than on high end boards and does never detect under/overshoot.