eBPF Sync

Plugin: ebpf.plugin Module: sync

Overview

Monitor syscall responsible to move data from memory to storage device.

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, CONFIG_HAVE_SYSCALL_TRACEPOINTS), files inside debugfs, 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 an internal kernel function monitored by this thread 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 Sync instance

These metrics show total number of calls to functions inside kernel.

This scope has no labels.

Metrics:

Metric	Dimensions	Unit
mem.file_sync	fsync, fdatasync	calls/s
mem.memory_map	msync	calls/s
mem.sync	sync, syncfs	calls/s
mem.file_segment	sync_file_range	calls/s

Alerts

The following alerts are available:

Alert name	On metric	Description
sync_freq	mem.sync	number of sync() system calls. Every call causes all pending modifications to filesystem metadata and cached file data to be written to the underlying filesystems.

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

Debug Filesystem

This thread needs to attach a tracepoint to monitor when a process schedule an exit event. To allow this specific feaure, it is necessary to mount debugfs (mount -t debugfs none /sys/kernel/debug).

Configuration

File

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

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/sync.conf

Options

This configuration file have two different sections. The [global] overwrites all default options, while [syscalls] allow user to select the syscall to monitor.

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
apps	Enable or disable integration with apps.plugin	no	no
cgroups	Enable or disable integration with cgroup.plugin	no	no
pid table size	Number of elements stored inside hash tables used to monitor calls per PID.	32768	no
ebpf type format	Define the file type to load an eBPF program. Three options are available: legacy (Attach only kprobe), co-re (Plugin tries to use trampoline when available), and auto (plugin check OS configuration before to load).	auto	no
ebpf co-re tracing	Select the attach method used by plugin when co-re is defined in previous option. Two options are available: trampoline (Option with lowest overhead), and probe (the same of legacy code).	trampoline	no
maps per core	Define how plugin will load their hash maps. When enabled (yes) plugin will load one hash table per core, instead to have centralized information.	yes	no
lifetime	Set default lifetime for thread when enabled by cloud.	300	no
sync	Enable or disable monitoring for syscall sync	yes	no
msync	Enable or disable monitoring for syscall msync	yes	no
fsync	Enable or disable monitoring for syscall fsync	yes	no
fdatasync	Enable or disable monitoring for syscall fdatasync	yes	no
syncfs	Enable or disable monitoring for syscall syncfs	yes	no
sync_file_range	Enable or disable monitoring for syscall sync_file_range	yes	no

Examples

There are no configuration examples.