Blog Posts

How To Install and Boot VMWare VSphere/ESXi from Persistent Memory (or not)

• How to

In a previous post I described how to install and boot Linux using only Persistent Memory, no SSDs are required. For this follow on post, I attempted to install VMWare VSphere/ESXi v7.0u2 onto the persistent memory.

TL;DR - It doesn’t work. The installer doesn’t list the PMem devices, and I was unable to find a way to manually select the PMem device(s).

I assume you followed the previous post to configure sector namespaces that we’ll use to install ESXi.

How To Install and Boot VMWare VSphere/ESXi from Persistent Memory (or not)

• How to

In a previous post I described how to install and boot Linux using only Persistent Memory, no SSDs are required. For this follow on post, I attempted to install VMWare VSphere/ESXi v7.0u2 onto the persistent memory.

TL;DR - It doesn’t work. The installer doesn’t list the PMem devices, and I was unable to find a way to manually select the PMem device(s).

I assume you followed the previous post to configure sector namespaces that we’ll use to install ESXi.

How to build an upstream Fedora Kernel from source

• Steve Scargall
• How to , Linux

I typically keep my Fedora system current, updating it once every week or two. More recently, I wanted to test the Idle Page Tracking feature, but this wasn’t enabled in the default kernel provided by Fedora.

# grep CONFIG_IDLE_PAGE_TRACKING /boot/config-$(uname -r)
# CONFIG_IDLE_PAGE_TRACKING is not set

To enable the feature, we need to build a custom kernel with the feature(s) we need. Thankfully, the process isn’t too difficult.

For this walk through, I’ll be building a customised version of the Fedora 32 kernel version I already have installed (5.8.7-200.fc32.x86_64), using some of the instructions from https://fedoraproject.org/wiki/Building_a_custom_kernel .

Linux Device Mapper WriteCache (dm-writecache) performance improvements in Linux Kernel 5.8

• Steve Scargall
• How to , Linux

The Linux ‘dm-writecache’ target allows for writeback caching of newly written data to an SSD or NVMe using persistent memory will achieve much better performance in Linux Kernel 5.8.

Red Hat developer Mikulas Patocka has been working to enhance the dm-writecache performance using Intel Optane Persistent Memory (PMem) as the cache device.

The performance optimization now queued for Linux 5.8 is making use of CLFLUSHOPT within dm-writecache when available instead of MOVNTI. CLFLUSHOPT is one of Intel’s persistent memory instructions that allows for optimized flushing of cache lines by supporting greater concurrency. The CLFLUSHOPT instruction has been supported on Intel servers since Skylake and on AMD since Zen.

"ipmctl show -memoryresources" returns "Error: GetMemoryResourcesInfo Failed"

• Steve Scargall
• Linux , Troubleshooting

Issue:

Running ipmctl show -memoryresources returns an error similar to the following:

# ipmctl show -memoryresources

Error: GetMemoryResourcesInfo Failed

Applies To:

• Linux & Microsoft Windows

• Intel Optane Persistent Memory

• ipmctl utility

Cause:

The Platform Configuration Data (PCD) is invalid or has been erased using a previously executed ipmctl delete -dimm -pcd command or the system has new persistent memory modules that have not been initialized yet.

A module with an empty PCD will show information similar to the following. This shows an example of PCD of DIMM ID 0x0001. To review the PCD for all modules in the system use ipmctl show -dimm -pcd.

Intel Optane Persistent Memory Modules report "Non-functional" state in ipmctl

• Steve Scargall
• Linux , Troubleshooting

Issue

Executing ipmctl show-dimm to get device information shows the persistent memory modules in a ‘Non-functional’ health state, eg:

# ipmctl show -dimm

 DimmID | Capacity | HealthState    | ActionRequired | LockState | FWVersion
=============================================================================
 0x0001 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x0011 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x0021 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x0101 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x0111 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x0121 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x1001 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x1011 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x1021 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x1101 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x1111 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A
 0x1121 | 0.0 GiB  | Non-functional | N/A            | N/A       | N/A

Other ipmctl commands may fail and return “No functional DIMMs in the system.”, eg:

How To Set Linux CPU Scaling Governor to Max Performance

• Steve Scargall
• How to , Linux

The majority of modern processors are capable of operating in a number of different clock frequency and voltage configurations, often referred to as Operating Performance Points or P-states (in ACPI terminology). As a rule, the higher the clock frequency and the higher the voltage, the more instructions can be retired by the CPU over a unit of time, but also the higher the clock frequency and the higher the voltage, the more energy is consumed over a unit of time (or the more power is drawn) by the CPU in the given P-state. Therefore there is a natural trade-off between the CPU capacity (the number of instructions that can be executed over a unit of time) and the power drawn by the CPU.

How To Verify Linux Kernel Support for Persistent Memory

• Steve Scargall
• How to , Linux

Linux Kernel support for persistent memory was first delivered in version 4.0 of the mainline kernel, however, it was not enabled by default until version 4.2.

If you use a Linux distribution that uses kernel 4.2 or later, or the distro backports features in to an older kernel, you will almost certainly have persistent memory support enabled by default. It is still worth verifying what features are enabled and disabled as this may vary by distro and release version for the very latest persistent memory features.