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# eBPF Cachestat


<img src="https://netdata.cloud/img/ebpf.jpg" width="150"/>


Plugin: ebpf-go.plugin
Module: cachestat

<img src="https://img.shields.io/badge/maintained%20by-Netdata-%2300ab44" />

## Overview

Monitor Linux page cache events giving users a general vision about how the kernel is manipulating files.

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. Netdata sets necessary permission during installation time.

eBPF Cachestat can be monitored further using the following other integrations:

- [Applications](/src/collectors/apps.plugin/integrations/applications.md)
- [Containers](/src/collectors/cgroups.plugin/integrations/containers.md)

### Default Behavior

#### Auto-Detection

The plugin checks kernel compilation flags (CONFIG_KPROBES, CONFIG_BPF, CONFIG_BPF_SYSCALL, CONFIG_BPF_JIT), presence of BTF files, and the configured object flavor 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 90-200ns per call on kernels that do not have BTF technology.

## 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 according to the 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 defined 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

#### Options

All options are defined inside section `[global]`.


<details open><summary>Config options</summary>



| Option | Description | Default | Required |
|:-----|:------------|:--------|:---------:|
| update every | Data collection frequency. This configuration value takes precedence over the runtime interval passed by pluginsd. | 10 | no |
| ebpf load mode | Legacy compatibility option. eBPFGo accepts `entry`; `return` is not supported and is ignored with a warning. | 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 object flavor | Select the cachestat object flavor to load. Available values are `arena`, `buffer ring` (also accepted as `buffer`), and `legacy` (also accepted as `tracing`). The default is `buffer`, and the collector falls back when the requested flavor is not available on the system. | buffer | 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 |
| btf path | Override the default BTF source directory. The collector checks this path for a vmlinux BTF file used by CO-RE loading. | /sys/kernel/btf | no |
| collect pid | Controls which PIDs are stored in the BPF hash tables. `real parent` stores only the real parent PID (lowest overhead); `parent` stores the immediate parent PID; `all` stores every PID used by the process (highest overhead). | real parent | no |
| lifetime | Set default lifetime for thread when enabled by cloud. | 300 | no |


</details>



#### via File

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


You can edit the configuration file using the [`edit-config`](https://github.com/netdata/netdata/blob/master/docs/netdata-agent/configuration/README.md#edit-configuration-files) script from the
Netdata [config directory](https://github.com/netdata/netdata/blob/master/docs/netdata-agent/configuration/README.md#locate-your-config-directory).

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

##### Examples
There are no configuration examples.



## Alerts

There are no alerts configured by default for this integration.



## 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 Cachestat instance

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

This scope has no labels.

Metrics:

| Metric | Description | Dimensions | Unit |
|:------|:------------|:----------|:----|
| mem.cachestat_ratio | Hit ratio | ratio | % |
| mem.cachestat_dirties | Number of dirty pages | dirty | page/s |
| mem.cachestat_hits | Number of accessed files | hit | hits/s |
| mem.cachestat_misses | Files out of page cache | miss | misses/s |
