Merge pull request containers#14903 from eriksjolund/add_performance_doc

[CI:DOCS] Add performance tutorial

docs/tutorials/README.md

@@ -35,3 +35,7 @@ A basic guide to common network setups with Podman
 **[Socket activation](socket_activation.md)**
 
 Learn how to run containers that support socket activation.
+
+**[Performance](performance.md)**
+
+Performance guide regarding Podman configuration and usage.

docs/tutorials/performance.md

@@ -0,0 +1,210 @@
+# Podman performance guide
+
+The performance of Podman may be influenced by a number of factors, such as,
+
+* the specified Podman command-line options and configuration
+* the OCI runtime
+* the host file system
+* the container image
+
+Changing any of these may or may not have any noticeable effect on the performance of Podman on your system.
+
+## Using a separate user account for benchmarking
+
+Some performance tips, such as using a different storage driver would require the user to run `podman system reset`,
+which erases all containers and container images for the user.
+Instead of benchmarking different alternatives in your own home directory, you could create a new user
+that afterwards can be removed.
+
+### Example: Specify the storage driver _vfs_ and run `/bin/true` in an Alpine container
+
+Interactively
+
+```
+sudo useradd testuser
+sudo machinectl testuser@
+podman pull docker.io/library/alpine
+/usr/bin/time -v podman --storage-driver=vfs run --rm docker.io/library/alpine /bin/true
+exit
+```
+
+Noninteractively
+
+```
+sudo useradd testuser
+systemd-run --machine=testuser@ --quiet --user --collect --pipe --wait \
+   podman --storage-driver=vfs pull docker.io/library/alpine
+systemd-run --machine=testuser@ --quiet --user --collect --pipe --wait \
+   /usr/bin/time -v podman --storage-driver=vfs run --rm docker.io/library/alpine /bin/true
+```
+
+The command `/usr/bin/time -v` measures and displays benchmarking information.
+
+## Performance considerations
+
+### Use a fast OCI runtime
+
+Podman uses an OCI runtime when running containers.
+The fastest OCI runtime is probably [__crun__](https://github.com/containers/crun).
+
+Check that you are using crun
+
+```
+$ podman info --format={{.Host.OCIRuntime.Name}}
+crun
+```
+
+To benchmark an OCI runtime, create a test user account and
+specify the OCI runtime path with [__--runtime__](https://docs.podman.io/en/latest/markdown/podman.1.html#runtime-value).
+
+### Choosing a storage driver
+
+The following storage drivers are listed from fastest to slowest:
+
+1. native overlayfs
+2. fuse-overlayfs
+3. vfs
+
+Using native overlayfs as an unprivileged user is only available for Podman version >= 3.1 on a Linux kernel version >= 5.12.
+
+To show the current storage driver
+
+```
+$ podman info -f {{.Store.GraphDriverName}}
+overlay
+$ podman info -f '{{index .Store.GraphStatus "Native Overlay Diff"}}'
+true
+```
+
+Storage driver   | Result of `podman info -f {{.Store.GraphDriverName}}` | Result of `podman info -f '{{index .Store.GraphStatus "Native Overlay Diff"}}`
+----             | ------                                                | -----
+native overlayfs | overlay                                               | true
+fuse-overlayfs   | overlay                                               | false
+VFS              | vfs                                                   | false
+
+Before changing the storage driver, running `podman system reset` is required.
+The command erases all containers and container images for the user.
+See the example above "_Using a separate user account for benchmarking_" for how to benchmark a storage driver in a separate test account.
+
+#### Specifying the storage driver with command-line options
+
+Storage driver   | Podman command
+----             | ------
+native overlayfs | `podman --storage-driver=overlayfs run ...`
+fuse-overlayfs   | `podman --storage-driver=overlayfs --storage-opt overlay.mount_program=/usr/bin/fuse-overlayfs run ...`
+VFS              | `podman --storage-driver=vfs run ...`
+
+#### Configuring the default storage driver
+
+The default storage driver can be configured in
+_/etc/containers/storage.conf_ and overridden by a user in
+_~/.config/containers/storage.conf_
+
+To configure native overlayfs:
+```
+[storage]
+driver = "overlay"
+```
+
+To configure fuse-overlayfs:
+```
+[storage]
+driver = "overlay"
+[storage.options.overlay]
+mount_program = "/usr/bin/fuse-overlayfs"
+```
+
+To configure VFS:
+```
+[storage]
+driver = "vfs"
+```
+
+See storage.conf(5) for all available configuration settings.
+
+### Network performance for rootless Podman
+
+When using rootless Podman, network traffic is normally passed through
+[slirp4netns](https://github.com/containers/podman/blob/main/docs/tutorials/basic_networking.md#slirp4netns).
+This comes with a performance penalty.
+
+You can avoid using slirp4netns in the following ways:
+
+* Use socket activation for listening network sockets. Communication over the activated socket does not pass through
+  slirp4netns, so it has the same performance characteristics as the normal network on the host.
+  Socket-activated services can be started and stopped in different ways:
+  + Let systemd start the service when the first client connects. Let the service terminate by itself after some time of inactivity.
+    Using a service on demand, can free up compute resources.
+  + Start the service explicitly (`systemctl --user enable foobar.service`). If the service is already
+    running when the first client connects, there will be no delay due to container startup.
+  The [socket activation tutorial](https://github.com/containers/podman/blob/main/docs/tutorials/socket_activation.md)
+  provides more information about socket activation support in Podman.
+
+* Use the network driver [_pasta_](https://passt.top/passt/about/#pasta). Pasta is under development and currently needs a patched Podman to run.
+
+* Set up the network manually as root. Create a bridge and virtual ethernet pair (VETH). See the [example](https://lists.podman.io/archives/list/[email protected]/thread/W6MCYO6RY5YFRTSUDAOEZA7SC2EFXRZE/) posted on the Podman mailing list. See also the section _DIY networking_ in [Podman-Rootless-Networking.pdf](https://podman.io/community/meeting/notes/2021-10-05/Podman-Rootless-Networking.pdf).
+
+* Use `--network=host`. No network namespace is created. The container will use the host’s network.
+  Note: By using `--network=host`, the container is given full access to local system services such as D-bus and is therefore considered insecure.
+
+### Lazy pulling of container images
+
+Podman supports lazy pulling for the following container image formats:
+
+* __zstd:chunked__
+
+* __eStargz__
+
+__zstd:chunked__ has better performance than __eStargz__.
+
+See the article [_Pull container images faster with partial pulls_](https://www.redhat.com/sysadmin/faster-container-image-pulls) by Giuseppe Scrivano and Dan Walsh.
+
+### Choosing a host file system
+
+Lazy pulling of container images can run more efficiently when the file system has reflink support. The file systems XFS and BTRFS have reflink support.
+
+### Option --log-driver
+
+The `podman run` option [__--log-driver__](https://docs.podman.io/en/latest/markdown/podman-run.1.html#log-driver-driver) specifies the logging driver for the container.
+
+If logging is not needed, consider using `--log-driver=none` to disable logging.
+
+### Reuse the package repository cache when building container images
+
+The first step of a container build is often to download metadata from
+the package repositories and post-process that data.
+
+To speed up container builds, you could prepare a directory on the host
+that contains the package metadata and then make the directory available
+to the container build by using an _overlay mount_.
+
+#### Example : Speed up _podman build_ by reusing the DNF metadata cache
+
+In this example the containers are based on Fedora 36.
+
+First create an empty directory on the host, for example *$HOME/dnf_cache_f36*.
+
+```
+$ mkdir $HOME/dnf_cache_f36
+```
+
+Fill the directory with the most recent __dnf__ metadata cache.
+
+```
+$ podman run --rm -v $HOME/dnf_cache_f36:/var/cache/dnf:Z registry.fedoraproject.org/fedora:36 dnf makecache
+```
+
+Create a new directory, for example, _$HOME/ctr_ and a file _$HOME/ctr/Containerfile_ with these contents
+
+```
+FROM registry.fedoraproject.org/fedora:36
+RUN dnf -y update && dnf -y install cowsay && dnf clean all
+```
+
+To build the Containerfile using the prepared metadata cache, provide the directory _$HOME/dnf_cache_f36_ as an _overlay mount_ (volume option `:O`)
+
+```
+$ podman build -v $HOME/dnf_cache_f36:/var/cache/dnf:O -t cowsay $HOME/ctr
+```
+
+The article [_Speeding up container image builds with Buildah_](https://www.redhat.com/sysadmin/speeding-container-buildah) by Dan Walsh provides more details.