278 lines
14 KiB
Markdown
278 lines
14 KiB
Markdown
# Performance Guide
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[TOC]
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gVisor is designed to provide a secure, virtualized environment while preserving
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key benefits of containerization, such as small fixed overheads and a dynamic
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resource footprint. For containerized infrastructure, this can provide a
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turn-key solution for sandboxing untrusted workloads: there are no changes to
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the fundamental resource model.
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gVisor imposes runtime costs over native containers. These costs come in two
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forms: additional cycles and memory usage, which may manifest as increased
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latency, reduced throughput or density, or not at all. In general, these costs
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come from two different sources.
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First, the existence of the [Sentry](../README.md#sentry) means that additional
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memory will be required, and application system calls must traverse additional
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layers of software. The design emphasizes
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[security](/docs/architecture_guide/security/) and therefore we chose to use a
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language for the Sentry that provides benefits in this domain but may not yet
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offer the raw performance of other choices. Costs imposed by these design
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choices are **structural costs**.
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Second, as gVisor is an independent implementation of the system call surface,
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many of the subsystems or specific calls are not as optimized as more mature
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implementations. A good example here is the network stack, which is continuing
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to evolve but does not support all the advanced recovery mechanisms offered by
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other stacks and is less CPU efficient. This is an **implementation cost** and
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is distinct from **structural costs**. Improvements here are ongoing and driven
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by the workloads that matter to gVisor users and contributors.
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This page provides a guide for understanding baseline performance, and calls out
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distinct **structural costs** and **implementation costs**, highlighting where
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improvements are possible and not possible.
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While we include a variety of workloads here, it’s worth emphasizing that gVisor
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may not be an appropriate solution for every workload, for reasons other than
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performance. For example, a sandbox may provide minimal benefit for a trusted
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database, since _user data would already be inside the sandbox_ and there is no
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need for an attacker to break out in the first place.
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## Methodology
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All data below was generated using the [benchmark tools][benchmark-tools]
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repository, and the machines under test are uniform [Google Compute Engine][gce]
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Virtual Machines (VMs) with the following specifications:
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Machine type: n1-standard-4 (broadwell)
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Image: Debian GNU/Linux 9 (stretch) 4.19.0-0
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BootDisk: 2048GB SSD persistent disk
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Through this document, `runsc` is used to indicate the runtime provided by
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gVisor. When relevant, we use the name `runsc-platform` to describe a specific
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[platform choice](/docs/architecture_guide/platforms/).
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**Except where specified, all tests below are conducted with the `ptrace`
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platform. The `ptrace` platform works everywhere and does not require hardware
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virtualization or kernel modifications but suffers from the highest structural
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costs by far. This platform is used to provide a clear understanding of the
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performance model, but in no way represents an ideal scenario. In the future,
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this guide will be extended to bare metal environments and include additional
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platforms.**
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## Memory access
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gVisor does not introduce any additional costs with respect to raw memory
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accesses. Page faults and other Operating System (OS) mechanisms are translated
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through the Sentry, but once mappings are installed and available to the
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application, there is no additional overhead.
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{% include graph.html id="sysbench-memory"
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url="/performance/sysbench-memory.csv" title="perf.py sysbench.memory
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--runtime=runc --runtime=runsc" %}
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The above figure demonstrates the memory transfer rate as measured by
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`sysbench`.
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## Memory usage
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The Sentry provides an additional layer of indirection, and it requires memory
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in order to store state associated with the application. This memory generally
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consists of a fixed component, plus an amount that varies with the usage of
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operating system resources (e.g. how many sockets or files are opened).
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For many use cases, fixed memory overheads are a primary concern. This may be
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because sandboxed containers handle a low volume of requests, and it is
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therefore important to achieve high densities for efficiency.
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{% include graph.html id="density" url="/performance/density.csv" title="perf.py
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density --runtime=runc --runtime=runsc" log="true" y_min="100000" %}
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The above figure demonstrates these costs based on three sample applications.
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This test is the result of running many instances of a container (50, or 5 in
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the case of redis) and calculating available memory on the host before and
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afterwards, and dividing the difference by the number of containers. This
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technique is used for measuring memory usage over the `usage_in_bytes` value of
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the container cgroup because we found that some container runtimes, other than
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`runc` and `runsc`, do not use an individual container cgroup.
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The first application is an instance of `sleep`: a trivial application that does
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nothing. The second application is a synthetic `node` application which imports
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a number of modules and listens for requests. The third application is a similar
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synthetic `ruby` application which does the same. Finally, we include an
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instance of `redis` storing approximately 1GB of data. In all cases, the sandbox
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itself is responsible for a small, mostly fixed amount of memory overhead.
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## CPU performance
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gVisor does not perform emulation or otherwise interfere with the raw execution
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of CPU instructions by the application. Therefore, there is no runtime cost
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imposed for CPU operations.
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{% include graph.html id="sysbench-cpu" url="/performance/sysbench-cpu.csv"
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title="perf.py sysbench.cpu --runtime=runc --runtime=runsc" %}
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The above figure demonstrates the `sysbench` measurement of CPU events per
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second. Events per second is based on a CPU-bound loop that calculates all prime
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numbers in a specified range. We note that `runsc` does not impose a performance
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penalty, as the code is executing natively in both cases.
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This has important consequences for classes of workloads that are often
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CPU-bound, such as data processing or machine learning. In these cases, `runsc`
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will similarly impose minimal runtime overhead.
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{% include graph.html id="tensorflow" url="/performance/tensorflow.csv"
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title="perf.py tensorflow --runtime=runc --runtime=runsc" %}
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For example, the above figure shows a sample TensorFlow workload, the
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[convolutional neural network example][cnn]. The time indicated includes the
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full start-up and run time for the workload, which trains a model.
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## System calls
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Some **structural costs** of gVisor are heavily influenced by the
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[platform choice](/docs/architecture_guide/platforms/), which implements system
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call interception. Today, gVisor supports a variety of platforms. These
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platforms present distinct performance, compatibility and security trade-offs.
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For example, the KVM platform has low overhead system call interception but runs
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poorly with nested virtualization.
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{% include graph.html id="syscall" url="/performance/syscall.csv" title="perf.py
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syscall --runtime=runc --runtime=runsc-ptrace --runtime=runsc-kvm" y_min="100"
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log="true" %}
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The above figure demonstrates the time required for a raw system call on various
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platforms. The test is implemented by a custom binary which performs a large
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number of system calls and calculates the average time required.
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This cost will principally impact applications that are system call bound, which
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tend to be high-performance data stores and static network services. In general,
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the impact of system call interception will be lower the more work an
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application does.
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{% include graph.html id="redis" url="/performance/redis.csv" title="perf.py
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redis --runtime=runc --runtime=runsc" %}
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For example, `redis` is an application that performs relatively little work in
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userspace: in general it reads from a connected socket, reads or modifies some
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data, and writes a result back to the socket. The above figure shows the results
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of running [comprehensive set of benchmarks][redis-benchmark]. We can see that
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small operations impose a large overhead, while larger operations, such as
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`LRANGE`, where more work is done in the application, have a smaller relative
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overhead.
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Some of these costs above are **structural costs**, and `redis` is likely to
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remain a challenging performance scenario. However, optimizing the
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[platform](/docs/architecture_guide/platforms/) will also have a dramatic
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impact.
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## Start-up time
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For many use cases, the ability to spin-up containers quickly and efficiently is
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important. A sandbox may be short-lived and perform minimal user work (e.g. a
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function invocation).
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{% include graph.html id="startup" url="/performance/startup.csv" title="perf.py
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startup --runtime=runc --runtime=runsc" %}
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The above figure indicates how total time required to start a container through
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[Docker][docker]. This benchmark uses three different applications. First, an
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alpine Linux-container that executes `true`. Second, a `node` application that
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loads a number of modules and binds an HTTP server. The time is measured by a
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successful request to the bound port. Finally, a `ruby` application that
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similarly loads a number of modules and binds an HTTP server.
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> Note: most of the time overhead above is associated Docker itself. This is
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> evident with the empty `runc` benchmark. To avoid these costs with `runsc`,
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> you may also consider using `runsc do` mode or invoking the
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> [OCI runtime](../user_guide/quick_start/oci.md) directly.
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## Network
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Networking is mostly bound by **implementation costs**, and gVisor's network
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stack is improving quickly.
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While typically not an important metric in practice for common sandbox use
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cases, nevertheless `iperf` is a common microbenchmark used to measure raw
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throughput.
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{% include graph.html id="iperf" url="/performance/iperf.csv" title="perf.py
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iperf --runtime=runc --runtime=runsc" %}
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The above figure shows the result of an `iperf` test between two instances. For
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the upload case, the specified runtime is used for the `iperf` client, and in
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the download case, the specified runtime is the server. A native runtime is
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always used for the other endpoint in the test.
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{% include graph.html id="applications" metric="requests_per_second"
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url="/performance/applications.csv" title="perf.py http.(node|ruby)
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--connections=25 --runtime=runc --runtime=runsc" %}
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The above figure shows the result of simple `node` and `ruby` web services that
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render a template upon receiving a request. Because these synthetic benchmarks
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do minimal work per request, much like the `redis` case, they suffer from high
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overheads. In practice, the more work an application does the smaller the impact
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of **structural costs** become.
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## File system
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Some aspects of file system performance are also reflective of **implementation
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costs**, and an area where gVisor's implementation is improving quickly.
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In terms of raw disk I/O, gVisor does not introduce significant fundamental
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overhead. For general file operations, gVisor introduces a small fixed overhead
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for data that transitions across the sandbox boundary. This manifests as
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**structural costs** in some cases, since these operations must be routed
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through the [Gofer](../README.md#gofer) as a result of our
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[Security Model](/docs/architecture_guide/security/), but in most cases are
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dominated by **implementation costs**, due to an internal
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[Virtual File System][vfs] (VFS) implementation that needs improvement.
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{% include graph.html id="fio-bw" url="/performance/fio.csv" title="perf.py fio
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--engine=sync --runtime=runc --runtime=runsc" log="true" %}
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The above figures demonstrate the results of `fio` for reads and writes to and
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from the disk. In this case, the disk quickly becomes the bottleneck and
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dominates other costs.
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{% include graph.html id="fio-tmpfs-bw" url="/performance/fio-tmpfs.csv"
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title="perf.py fio --engine=sync --runtime=runc --tmpfs=True --runtime=runsc"
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log="true" %}
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The above figure shows the raw I/O performance of using a `tmpfs` mount which is
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sandbox-internal in the case of `runsc`. Generally these operations are
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similarly bound to the cost of copying around data in-memory, and we don't see
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the cost of VFS operations.
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{% include graph.html id="httpd100k" metric="transfer_rate"
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url="/performance/httpd100k.csv" title="perf.py http.httpd --connections=1
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--connections=5 --connections=10 --connections=25 --runtime=runc
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--runtime=runsc" %}
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The high costs of VFS operations can manifest in benchmarks that execute many
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such operations in the hot path for serving requests, for example. The above
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figure shows the result of using gVisor to serve small pieces of static content
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with predictably poor results. This workload represents `apache` serving a
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single file sized 100k from the container image to a client running
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[ApacheBench][ab] with varying levels of concurrency. The high overhead comes
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principally from the VFS implementation that needs improvement, with several
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internal serialization points (since all requests are reading the same file).
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Note that some of some of network stack performance issues also impact this
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benchmark.
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{% include graph.html id="ffmpeg" url="/performance/ffmpeg.csv" title="perf.py
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media.ffmpeg --runtime=runc --runtime=runsc" %}
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For benchmarks that are bound by raw disk I/O and a mix of compute, file system
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operations are less of an issue. The above figure shows the total time required
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for an `ffmpeg` container to start, load and transcode a 27MB input video.
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[ab]: https://en.wikipedia.org/wiki/ApacheBench
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[benchmark-tools]: https://github.com/google/gvisor/tree/master/benchmarks
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[gce]: https://cloud.google.com/compute/
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[cnn]: https://github.com/aymericdamien/TensorFlow-Examples/blob/master/examples/3_NeuralNetworks/convolutional_network.py
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[docker]: https://docker.io
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[redis-benchmark]: https://redis.io/topics/benchmarks
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[vfs]: https://en.wikipedia.org/wiki/Virtual_file_system
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