eBPF MDflush

Plugin: ebpf.plugin Module: mdflush

Overview

Monitor when flush events happen between disks.

Attach tracing (kprobe, trampoline) to internal kernel functions according options used to compile kernel.

This collector is only supported on the following platforms:

• Linux

This collector supports collecting metrics from multiple instances of this integration, including remote instances.

The plugin needs setuid because it loads data inside kernel. Netada sets necessary permission during installation time.

Default Behavior

Auto-Detection

The plugin checks kernel compilation flags (CONFIG_KPROBES, CONFIG_BPF, CONFIG_BPF_SYSCALL, CONFIG_BPF_JIT) and presence of BTF files to decide which eBPF program will be attached.

Limits

The default configuration for this integration does not impose any limits on data collection.

Performance Impact

This thread will add overhead every time that md_flush_request is called. The estimated additional period of time is between 90-200ms per call on kernels that do not have BTF technology.

Metrics

Metrics grouped by scope.

The scope defines the instance that the metric belongs to. An instance is uniquely identified by a set of labels.

Per eBPF MDflush instance

Number of times md_flush_request was called since last time.

This scope has no labels.

Metrics:

Metric	Dimensions	Unit
mdstat.mdstat_flush	disk	flushes

Alerts

There are no alerts configured by default for this integration.

Setup

Prerequisites

Compile kernel

Check if your kernel was compiled with necessary options (CONFIG_KPROBES, CONFIG_BPF, CONFIG_BPF_SYSCALL, CONFIG_BPF_JIT) in /proc/config.gz or inside /boot/config file. Some cited names can be different accoring preferences of Linux distributions. When you do not have options set, it is necessary to get the kernel source code from https://kernel.org or a kernel package from your distribution, this last is preferred. The kernel compilation has a well definedd pattern, but distributions can deliver their configuration files with different names.

Now follow steps:

1. Copy the configuration file to /usr/src/linux/.config.
2. Select the necessary options: make oldconfig
3. Compile your kernel image: make bzImage
4. Compile your modules: make modules
5. Copy your new kernel image for boot loader directory
6. Install the new modules: make modules_install
7. Generate an initial ramdisk image (initrd) if it is necessary.
8. Update your boot loader

Configuration

File

The configuration file name for this integration is ebpf.d/mdflush.conf.

The file format is a modified INI syntax. The general structure is:

[section1]
    option1 = some value
    option2 = some other value

[section2]
    option3 = some third value

You can edit the configuration file using the edit-config script from the Netdata config directory.

cd /etc/netdata 2>/dev/null || cd /opt/netdata/etc/netdata
sudo ./edit-config ebpf.d/mdflush.conf

Options

All options are defined inside section [global].

Config options

Name	Description	Default	Required
update every	Data collection frequency.	5	no
ebpf load mode	Define whether plugin will monitor the call (entry) for the functions or it will also monitor the return (return).	entry	no
lifetime	Set default lifetime for thread when enabled by cloud.	300	no

Examples

There are no configuration examples.