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diff --git a/content/docs/architecture_guide/performance.md b/content/docs/architecture_guide/performance.md new file mode 100644 index 000000000..58339dffb --- /dev/null +++ b/content/docs/architecture_guide/performance.md @@ -0,0 +1,245 @@ ++++ +title = "Performance Guide" +weight = 30 ++++ +gVisor is designed to provide a secure, virtualized environment while preserving +key benefits of containerization, such as small fixed overheads and a dynamic +resource footprint. For containerized infrastructure, this can provide an "easy +button" for sandboxing untrusted workloads: there are no changes to the +fundamental resource model. + +gVisor imposes runtime costs over native containers. These costs come in two +forms: additional cycles and memory usage, which may manifest as increased +latency, reduced throughput or density, or not at all. In general, these costs +come from two different sources. + +First, the existence of the [Sentry](../) means that additional memory will be +required, and application system calls must traverse additional layers of +software. The design emphasizes [security](../security/) and therefore we chose +to use a language for the Sentry that provides benefits in this domain but may +not yet offer the raw performance of other choices. Costs imposed by these +design choices are **structural costs**. + +Second, as gVisor is an independent implementation of the system call surface, +many of the subsystems or specific calls are not as optimized as more mature +implementations. A good example here is the network stack, which is continuing +to evolve but does not support all the advanced recovery mechanisms offered by +other stacks and is less CPU efficient. This an **implementation cost** and is +distinct from **structural costs**. Improvements here are ongoing and driven by +the workloads that matter to gVisor users and contributors. + +This page provides a guide for understanding baseline performance, and calls out +distint **structural costs** and **implementation costs**, highlighting where +improvements are possible and not possible. + +While we include a variety of workloads here, it’s worth emphasizing that gVisor +may not be an appropriate solution for every workload, for reasons other than +performance. For example, a sandbox is likely to provide minimal benefit for +your database, since *all your user data would already be inside the sandbox* +and there is no need for an attacker to break out in the first place. + +## Methodology + +All data below was generated using the [benchmark tools][benchmark-tools] +repository, and the machines under test are uniform [Google Compute Engine][gce] +Virtual Machines (VMs) with the following specifications: + +``` +Machine type: n1-standard-4 (broadwell) +Image: Debian GNU/Linux 9 (stretch) 4.19.0-0 +BootDisk: 2048GB SSD persistent disk +``` + +Through this document, `runsc` is used to indicate the runtime provided by +gVisor. When relevant, we use the name `runsc-platform` to describe a specific +[platform choice](../overview/). + +**Except where specified, all tests below are conducted with the `ptrace` +platform. The `ptrace` platform works everywhere and does not require hardware +virtualization or kernel modifications but suffers from the highest structural +costs by far. This platform is used to provide a clear understanding of the +performance model, but in no way represents an ideal scenario. In the future, +this guide will be extended to bare metal environments and include additional +platforms.** + +## Memory access + +gVisor does not introduce any additional costs with respect to raw memory +accesses. Page faults are other Operating System (OS) mechanisms are translated +through the Sentry, but once mappings are installed and available to the +application, there is no additional overhead. + +{{< graph id="sysbench-memory" url="/performance/sysbench-memory.csv" title="perf.py sysbench.memory --runtime=runc --runtime=runsc" >}} + +The above figure demonstrates the memory transfer rate as measured by +`sysbench`. + +## Memory usage + +The Sentry provides an additional layer of indirection, and it requires memory +in order to store state associated with the application. This memory generally +consists of a fixed component, plus an amount that varies with the usage of +operating system resources (e.g. how many sockets or files are opened). + +For many use cases, fixed memory overheads are a primary concern. This may be +because sandboxed containers handle a low volume of requests, and it is +therefore important to achieve high densities for efficiency. + +{{< graph id="density" url="/performance/density.csv" title="perf.py density --runtime=runc --runtime=runsc" >}} + +The above figure demonstrates these costs based on three sample applications. +This test is the result of running many instances of a container (typically 50) +and calculating available memory on the host before and afterwards, and dividing +the difference by the number of containers. + +The first application is an instance of `sleep`: a trivial application that does +nothing. The second application is a synthetic `node` application which imports +a number of modules and listens for requests. The third application is a similar +synthetic `ruby` application which does the same. + +## CPU performance + +gVisor does not perform emulation or otherwise interfere with the raw execution +of CPU instructions by the application. Therefore, there is no runtime cost +imposed for CPU operations. + +{{< graph id="sysbench-cpu" url="/performance/sysbench-cpu.csv" title="perf.py sysbench.cpu --runtime=runc --runtime=runsc" >}} + +The above figure demonstrates the `sysbench` measurement of CPU events per +second. Events per second is based on a CPU-bound loop that calculates all prime +numbers in a specified range. We note that `runsc` does not impose substantial +degradation, as the code is executing natively in both cases. + +This has important consequences for classes of workloads that are often +CPU-bound, such as data processing or machine learning. In these cases, `runsc` +will similarly impose minimal runtime overhead. + +{{< graph id="tensorflow" url="/performance/tensorflow.csv" title="perf.py tensorflow --runtime=runc --runtime=runsc" >}} + +For example, the above figure shows a sample TensorFlow workload, the +[convolutional neural network example][cnn]. The time indicated includes the +full start-up and run time for the workload, which trains a model. + +## System calls + +Some **structural costs** of gVisor are heavily influenced by the [platform +choice](../overview/), which implements system call interception. Today, gVisor +supports a variety of platforms. These platforms present distinct performance, +compatibility and security trade-offs. For example, the KVM platform has low +overhead system call interception but runs poorly with nested virtualization. + +{{< graph id="syscall" url="/performance/syscall.csv" title="perf.py syscall --runtime=runc --runtime=runsc-ptrace --runtime=runsc-kvm" log="true" >}} + +The above figure demonstrates the time required for a raw system call on various +platforms. The test is implemented by a custom binary which performs a large +number of system calls and calculates the average time required. + +This cost will principally impact applications that are system call bound, which +tend to be high-performance data stores and static network services. In general, +the impact of system call interception will be lower the more work an +application does. + +{{< graph id="redis" url="/performance/redis.csv" title="perf.py redis --runtime=runc --runtime=runsc" >}} + +For example, `redis` is an application that performs relatively little work in +userspace: in general it reads from a connected socket, reads or modifies some +data, and writes a result back to the socket. The above figure shows the results +of running [comprehensive set of benchmarks][redis-benchmark]. We can see that +small operations impose a large operation, while larger operations, such as +`LRANGE`, where more work is done in the application, have a smaller relative +overhead. + +Some of these costs above are **structural costs**, and `redis` is likely to +remain a challenging performance scenario. However, optimizing the +[platform](../overview) will also have a dramatic impact. + +## Start-up time + +For many use cases, the ability to spin-up containers quickly and efficiently is +important. A sandbox may be short-lived and perform minimal user work (e.g. a +function invocation). + +{{< graph id="startup" url="/performance/startup.csv" title="perf.py startup --runtime=runc --runtime=runsc" >}} + +The above figure indicates how total time required to start a container through +[Docker][docker]. This benchmark uses three different applications. First, an +alpine Linux-container that executes `true`. Second, a `node` application that +loads a number of modules and binds an HTTP server. The time is measured by a +successful request to the bound port. Finally, a `ruby` application that +similarly loads a number of modules and binds an HTTP server. + +## Network + +Networking is mostly bound by **implementation costs**, and gVisor's network stack +is improving quickly. + +While typically not an important metric in practice for common sandbox use +cases, nevertheless `iperf` is a common microbenchmark used to measure raw +throughput. + +{{< graph id="iperf" url="/performance/iperf.csv" title="perf.py iperf --runtime=runc --runtime=runsc" >}} + +The above figure shows the result of an `iperf` test between two instances. For +the upload case, the specified runtime is used for the `iperf` client, and in +the download case, the specified runtime is the server. A native runtime is +always used for the other endpoint in the test. + +{{< graph id="applications" metric="requests_per_second" url="/performance/applications.csv" title="perf.py http.(node|ruby) --connections=25 --runtime=runc --runtime=runsc" >}} + +The above figure shows the result of simple `node` and `ruby` web services that +render a template upon receiving a request. Because these synthetic benchmarks +do minimal work per request, must like the `redis` case, they suffer from high +overheads. In practice, the more work an application does the smaller the impact +of **structural costs** become. + +## File system + +Some aspects of file system performance are also reflective of **implementation +costs**, and an area where gVisor's implementation is improving quickly. + +In terms of raw disk I/O, gVisor does not introduce significant fundamental +overhead. For general file operations, gVisor introduces a small fixed overhead +for data that transitions across the sandbox boundary. This manifests as +**structural costs** in some cases, since these operations must be routed +through the [Gofer](../) as a result of our [security model](../security/), but +in most cases are dominated by **implementation costs**, due to an internal +[Virtual File System][vfs] (VFS) implementation the needs improvement. + +{{< graph id="fio-bw" url="/performance/fio.csv" title="perf.py fio --engine=sync --runtime=runc --runtime=runsc" >}} + +The above figures demonstrate the results of `fio` for reads and writes to and +from the disk. In this case, the disk quickly becomes the bottleneck and +dominates other costs. + +{{< graph id="fio-tmpfs-bw" url="/performance/fio-tmpfs.csv" title="perf.py fio --engine=sync --runtime=runc --tmpfs=True --runtime=runsc" >}} + +The above figure shows the raw I/O performance of using a `tmpfs` mount which is +sandbox-internal in the case of `runsc`. Generally these operations are +similarly bound to the cost of copying around data in-memory, and we don't see +the cost of VFS operations. + +{{< graph id="httpd100k" metric="transfer_rate" url="/performance/httpd100k.csv" title="perf.py http.httpd --connections=1 --connections=5 --connections=10 --connections=25 --runtime=runc --runtime=runsc" >}} + +The high costs of VFS operations can manifest in benchmarks that execute many +such operations in the hot path for serviing requests, for example. The above +figure shows the result of using gVisor to serve small pieces of static content +with predictably poor results. This workload represents `apache` serving a +single file sized 100k to a client running [ApacheBench][ab] with varying levels +of concurrency. The high overhead comes principles from a VFS implementation +needs improvement, with several internal serialization points (since all +requests are reading the same file). Note that some of some of network stack +performance issues also impact this benchmark. + +{{< graph id="ffmpeg" url="/performance/ffmpeg.csv" title="perf.py media.ffmpeg --runtime=runc --runtime=runsc" >}} + +For benchmarks that are bound by raw disk I/O and a mix of compute, file system +operations are less of an issue. The above figure shows the total time required +for an `ffmpeg` container to start, load and transcode an input video. + +[ab]: https://en.wikipedia.org/wiki/ApacheBench +[benchmark-tools]: https://gvisor.googlesource.com/benchmark-tools +[gce]: https://cloud.google.com/compute/ +[cnn]: https://github.com/aymericdamien/TensorFlow-Examples/blob/master/examples/3_NeuralNetworks/convolutional_network.py +[docker]: https://docker.io +[redis-benchmark]: https://redis.io/topics/benchmarks +[vfs]: https://en.wikipedia.org/wiki/Virtual_file_system |