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Wasp: micro-hypervisor that enables lightweight, isolated virtines


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Build Status License: MIT DOI


Wasp is an embeddable micro-hypervisor designed to support virtines, lightweight isolated execution contexts for individual functions. Virtines can either be created manually by invoking a runtime API, or automatically by using our Clang/LLVM compiler extensions. In the latter case, a developer can create a virtine by simply adding a keyword to a C function:

virtine int foo(int arg) {
	// code


Experimental Platform in the Paper

Note that the experiments in the paper were run on a Dell PowerEdge R6415 running Linux, specifically Fedora Server 34 with stock kernel version 5.9.12. This machine has an AMD EPYC 7281 (Naples; 16 cores; 2.69 GHz) CPU with 32 GB DDR4. We disabled hyperthreading, turbo boost, and DVFS to mitigate measurement noise. We used gcc 10.2.1 to compile Wasp (C/C++), clang 10.0.1 for our C-based virtine language extensions, and NASM v2.14 for assembly-only virtines. The data and plots used in the paper can be found in `data_example/

Build Instructions

Environment Setup

Wasp can be built and evaluated on any Linux x86 hardware that supports hardware virtualization through KVM. For evaluating the artifacts, we recommend an allocation on Cloudlab or Chameleon Cloud, as outlined below:

Cloudlab Configuration:

  • Apply for a Cloudlab account if you do not have one
  • Once logged in, Click Experiments then Create Experiment Profile
  • Upload the cloudlab.profile file provided in the root of this repo
  • Create the instance using that profile and SSH into it following cloudlab's docs

Chameleon Configuration:

  • Apply for a Chameleon account if you do not already have one.
  • Allocate a lease for one host (any x86 host with virtualization hardware should do, though we've tested on the default Haswell and Skylake nodes).
  • Select "Images" from the side bar and search for the "CC-Ubuntu20.04". Create an instance from this image by selecting "Launch" on the right. Tie this instance to the lease you created before under the "Reservation" drop-down. Make sure you set up a key pair and a floating IP so you can ssh to the instance.
  • Once the instance launches, ssh to it using the default Chameleon account (e.g., ssh cc@

Now you can proceed to building and running Wasp, described below.


The following packages are necessary to get Wasp running:

  • nasm
  • libcurl dev headers (libcurl-dev on recent Ubuntu is an aliased package; we had to use libcurl4-openssl-dev)
  • clang version 10 or newer
  • llvm and llvm-dev version 10 or newer
  • cmake version 12 or newer
  • python3.8-venv (for plotting)
  • openssl (only for OpenSSL example)

Additionally, you must be on a Linux box with KVM support (you can check with lsmod | grep kvm), i.e., a baremetal machine or one that supports nested virtualization. Wasp only support x86_64 (Intel, AMD) chips that have hardware virtualization extensions at the moment.

For example, on an Ubuntu 20.04 LTS machine:

sudo apt update
sudo apt install -y cmake nasm llvm llvm-dev clang clang-10 libcurl4-openssl-dev python3.8-venv openssl

If the cmake version installed (cmake --version) is less than 10, you can install the latest version as follows:

wget -O - 2>/dev/null | sudo apt-key add -
sudo apt-add-repository 'deb bionic main'
sudo apt-get update
sudo apt install --reinstall cmake

If llvm is also not the required version installed (llvm-config --version), update it as follows:

wget --no-check-certificate -O - | sudo apt-key add -
sudo add-apt-repository 'deb   llvm-toolchain-bionic-10  main'
sudo apt update && sudo apt-get install llvm-10 lldb-10 llvm-10-dev libllvm10 llvm-10-runtime
sudo update-alternatives --install /usr/bin/llvm-config llvm-config /usr/bin/llvm-config-6.0 6
sudo update-alternatives --install /usr/bin/llvm-config llvm-config /usr/bin/llvm-config-10 10
sudo update-alternatives --config llvm-config

N.B.: in the previous command lines, llvm-6.0 is the default version.

Building and Installing

git clone
cd wasp
sudo make install

The build should take less than a minute or so. make install simply copies the resulting binaries to /usr/local/{lib,bin,include}, and will not run any programs other than mkdir and install.

Running Virtine Tests

To ensure Wasp is functional, we have included a "smoke test" in the repo. You can run it like so (it should complete pretty much immediately):

make smoketest

If the smoketest doesn't panic, Wasp is functional at this point. We tested this most recently on Chameleon Cloud Ubuntu 20.04.3 LTS (baremetal Skylake, 48 cores, Xeon Gold 6126) with Linux kernel version 5.4.0-91-generic.

If the smoke test does panic, it may be because /dev/kvm is owned by root. You probably want to add your user to the kvm group (e.g., sudo usermod -a -G kvm <user>). An alternative is to change permissions on /dev/kvm when gathering the artifacts. To do so, you can run sudo chmod 666 /dev/kvm, though you'll probably want to restore these permissions when you're done building the artifact.

Reproducing Paper Results

To re-run the experiments and reproduce relevant figures from the paper, simply run:

make artifacts.tar

This will produce a .tar archive containing all relevant figures and data in artifacts.tar. It should take about 5 minutes to reproduce all results and plots this way. Here is what is included from the paper:

  • Context creation experiment (fig8.pdf); Figures 2 and 8 from the paper. Figure 8 is a superset of Figure 2.
  • Boot time breakdown (data/table1.csv); Table 1 from the paper.
  • Mode latency experiment (fig3.pdf); Figure 3 from the paper. Note that the version if this figure in the paper has a false origin; the plot generated here does not.
  • Echo server boot latency (fig4.pdf); Figure 4 from the paper.
  • Virtine creation latency microbenchmark (fig11.pdf); Figure 11 from the paper.
  • Effect of image size on virtine start-up latency (fig12.pdf); Figure 12 from the paper.
  • Virtine HTTP server performance (fig13_tput.pdf, fig13_lat.pdf); Figure 13 from the paper.
  • OpenSSL data (data/openssl.txt and data/openssl_baseline.txt); Section 6.4 from the paper.
  • JavaScript virtines performance (fig14.pdf); Figure 14 from the paper.

If you would like to run a single experiment, simply run make data_figX where X is the id of the figure (fig14.pdf uses data_fig14, fig13_lat.pdf uses data_fig13_lat).

Due to the nature of microarchitectural differences across CPUs, the data produced from some of these tests will vary slightly from machine to machine. In particular, we have noticed that Figures 3 and 8 and Table 1 show some discrepancies between AMD and Intel; we also see some variance across microarchitectural generations. Once you've collected results, you can compare them to some of the reference data we've collected in the data_example directory. See here for more.

Embedding Wasp

Wasp can be used two ways: as a library (which the programmer invokes through API calls) or as a compiler extension. Directly interfacing with Wasp can provide higher control over the execution of a virtine leading to lower overheads. Wasp's compiler extensions ease development significantly, but result in higher overheads and larger binaries due to their general-purpose functionality.

Direct API Access

Wasp exposes a simple API to construct a virtine in <wasp/Virtine.h>. You'll notice that the interface does not assume anything about the operation of the particular virtine, including how it is built. When interfacing with the wasp API directly, virtine compilation and invocation is up to the developer. An example of some minimal virtine code, as well as the code to invoke it looks like this:

// host.cpp
#include <wasp/Virtine.h>

int main(int argc, char **argv) {
	wasp::Virtine virtine;
	// allocate 32kb to the virtine
	// load a flat binary into the virtine at address 0x1000
	virtine.load_binary("virtine.bin", 0x1000);
	while (1) {
		// run the virtine until it exits by some mechanism
		//   (there will eventually be a timeout :^) )
		auto res =;
		if (res == wasp::ExitReason::HyperCall) {
			// handle the hypercall by interfacing with the registers
		if (res == wasp::ExitReason::Exited) break;
	return 0;

Here is a very simple virtine written in assembly:

;; virtine.asm
[org 0x8000]
global _start
	;; magic exit hypercall
	out 0xFA, eax

In this case, the developer must write and compile the virtine code on their own. In this example, the virtine's image (virtine.bin) can be assembled from the above code using nasm which will produce a 3 byte binary.

The final application can be compiled and run as follows:

nasm -fbin virtine.asm -o virtine.bin
g++ host.cpp -o host -lwasp

This should produce no output. The virtine will simply exit immediately. See the test/ directory for some more concrete examples. (test/js/host.cpp showcases most of the available API functionality).

To improve performance, Wasp provides caching mechanisms via wasp::Cache. If the above host.cpp is rewritten with caching, only a few things change:

// host.cpp
#include <wasp/Virtine.h>
#include <wasp/Cache.h>

int main(int argc, char **argv) {

	// allocate a cache of virtines that all have 16 pages of memory
	wasp::Cache cache(4096 * 16);

	// load the binary on the cache, not each virtine
	cache.load_binary("virtine.bin", 0x8000);

	// pre-provision 12 virtines (arbitrarially)

	// get a fresh virtine from the cache
	wasp::Virtine *v = cache.get();
	while (1) {
		// run the virtine, 
		auto res = v->run();
		if (res == wasp::ExitReason::HyperCall) {
			// handle the hypercall by interfacing with the registers
		if (res == wasp::ExitReason::Exited) break;
	// return the virtine once we are done
	return 0;

Virtine Compiler Extension (vcc)

The easiest way to use virtines is through vcc, which once built and installed allows existing C programs to run in context using only a simple keyword. A trivial example looks like this:

// main.c
#include <virtine.h>
#include <stdio.h>

virtine int square(int x) {
	return x * x;

int main(int argc, char **argv) {
	printf("%d\n", square(3));
	return 0;

If compiled with vcc (a drop-in for clang/gcc) a virtine for square() will be spawned and executed whenever square is invoked. By default, the virtine utilizes snapshotting to decrease start-up latencies. This can be disabled by defining the environment variable WASP_NO_SNAPSHOT=1 if you wish to see its effect. The compiler extension is currently in its early stages, and suffers from much of the weaknesses that a typical C compiler might have (no full program analysis, pointer aliasing, inability to inline functions from other C files, unsized pointers, etc.), but we imagine a future where a high-level language like SML may solve many of those problems.

Code Structure

All of the wasp runtime is implemented in src/ and include/, the LLVM pass is implemented in pass/, and test/ contains a set of tests which produce the data from the paper. The data_example directory contains example data gathered from a few machines. For example AMD-EPYC-7302P-cloudlab-c6525-25g/ contains the data gathered from the machine using the cloudlab.profile, and Intel-XEON-Gold-6126-chameleon is from an allocation on chameleon. See data_example/ for more details on each machine's hadware and software.


Wasp and the virtines codebase were made possible with support from the United States National Science Foundation (NSF) via grants CNS-1730689, REU-1757964, CNS-1718252, and CNS-1763612.


The Wasp/virtines codebase is currently maintained by Nicholas Wanninger (ncw [at] u [dot] northwestern [dot] edu).