Public bug reported:
## Summary
DDR5 memory configured for 6000 MT/s via EXPO profile runs at 4800 MT/s
(JEDEC base speed) under Linux, while the same hardware runs correctly
at 6000 MT/s under Windows 11.
## System Information
cat /proc/version_signature
Ubuntu 6.14.0-37.37~24.04.1-generic 6.14.11
- **CPU**: AMD Ryzen 9 9950X3D 16-Core Processor
- **Microcode**: 0xb404032
- **Motherboard**: ASUS ROG Crosshair X870E Hero
- **BIOS Version**: 1715 (2025-09-19)
- **Memory**: Corsair Dominator Titanium DDR5-6000 CL30 64GB (2×32GB)
- Part Number: CMP64GX5M2B6000Z30
- Configuration: Dual Channel, slots A2/B2
- **OS**: Linux Mint 22.2 (Ubuntu Noble base)
- **Kernel**: 6.14.0-37-generic (also tested 6.14.0-29 and 6.14.0-36)
- **Also tested**: Fedora 41 Live USB (same issue)
## Problem Description
### Expected behavior
Memory should run at 6000 MT/s as configured in BIOS via EXPO I profile,
providing ~80-90 GB/s memory bandwidth.
### Actual behavior
Memory runs at 4800 MT/s (JEDEC base speed), providing only ~27 GB/s memory
bandwidth.
### Evidence
**dmidecode output shows the discrepancy:**
```
Speed: 4800 MT/s
Configured Memory Speed: 6000 MT/s
```
The BIOS requests 6000 MT/s but Linux operates at 4800 MT/s.
**Memory bandwidth benchmark (mbw):**
```
AVG Method: MCBLOCK Elapsed: 0.01882 MiB: 512.00000 Copy: 27204.812 MiB/s
```
Expected for DDR5-6000 dual channel: ~80,000-90,000 MiB/s
**Windows 11 on same hardware:**
- CPU-Z confirms 3000 MHz (6000 MT/s)
- Memory bandwidth matches expected values
## Steps to Reproduce
1. Configure DDR5 memory with EXPO/XMP profile in ASUS X870E BIOS
2. Verify memory runs at configured speed under Windows (works correctly)
3. Boot Linux (any recent kernel 6.14.x)
4. Check memory speed: `sudo dmidecode -t memory | grep Speed`
5. Verify bandwidth: `mbw -n 5 512`
## Testing Performed
- [x] Tested multiple kernel versions (6.14.0-29, 6.14.0-36, 6.14.0-37) - all
affected
- [x] Tested Fedora 41 Live USB - same issue
- [x] Warm reboot from Windows (where RAM runs at 6000) to Linux - still drops
to 4800
- [x] Disabled Fast Boot in BIOS - no change
- [x] Set OS Type to "Other OS" - no change
- [x] Enabled DDR5 Nitro Mode - no change
- [x] Tested `amd_iommu=off` kernel parameter - no change
- [x] Blacklisted `edac_mce_amd` module - no change
- [x] Verified power profile (performance mode) - no change
## Relevant dmesg output
```
[ 5.479836] spd5118 1-0051: DDR5 temperature sensor: vendor 0x0b:0x10
revision 2.3
[ 5.483306] spd5118 1-0053: DDR5 temperature sensor: vendor 0x0b:0x10
revision 2.3
[ 6.725966] amd_atl: AMD Address Translation Library initialized
[ 6.734481] [drm] RAM width 128bits DDR5
```
No errors or warnings related to memory frequency.
## Loaded AMD-related modules
```
amdgpu, amd_atl, amdxcp, edac_mce_amd, kvm_amd, ccp, amd_3d_vcache, gpio_amdpt
```
## Kernel command line
```
BOOT_IMAGE=/boot/vmlinuz-6.14.0-37-generic root=UUID=xxx ro quiet splash
```
## Additional Information
This appears to be specific to Linux kernel behavior with AMD X870E chipset
and/or Ryzen 9000X3D series. The hardware is confirmed working correctly under
Windows 11, ruling out:
- Defective memory modules
- Weak IMC (Integrated Memory Controller)
- BIOS misconfiguration
- Motherboard issues
The issue persists across distributions (Linux Mint/Ubuntu and Fedora),
pointing to a kernel-level problem with memory frequency initialization
or ACPI/firmware interaction on this platform.
## Possible areas to investigate
1. AMD memory controller driver initialization
2. ACPI memory configuration tables interpretation
3. SPD/EXPO profile reading and application
4. X870E chipset specific memory handling
5. Ryzen 9000X3D series specific behavior
## Impact
Significant performance degradation (~70% loss of memory bandwidth)
affects all memory-intensive workloads under Linux.
** Affects: linux (Ubuntu)
Importance: Undecided
Status: New
** Attachment added: "lspci-vnvn.log"
https://bugs.launchpad.net/bugs/2135267/+attachment/5933352/+files/lspci-vnvn.log
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https://bugs.launchpad.net/bugs/2135267
Title:
DDR5 memory stuck at 4800 MT/s instead of configured 6000 MT/s (EXPO)
on AMD X870E + Ryzen 9950X3D
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