README.md

Windows User-Mode Scheduling (UMS)

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Introduction

The UMS (User-Mode Scheduling) is a feature added to Windows 7 and later, but only works in 64bit versions. It enable applications to schedule their own threads in their own custom policy. In this way, it provides the capability of fiber/coroutine, but in the form of native thread.

We compare the performance of UMS with those of native thread and fiber, using a very simple implementation.

Build

1. Install CMake and Visual Studio in 64bit Windows (7 or later).

2. In cmd, generate the VS project.

mkdir build
cd build
cmake ..

3. Open Windows-UMS.sln in Visual Studio.

4. Choose Release + x64 configuration, and Generate Solutions

Run

1. Run UMS version

Release\ms-example.exe <number-of-threads> <num-of-yields>

2. Run Native thread version

Release\thread-example.exe <number-of-threads> <num-of-yields>

3. Run Fiber version

Release\fiber-example.exe <number-of-threads> <num-of-yields>

Performance comparison

On my laptop (Lenovo Thinkpad X270 with Intel i5-6200U and 8G memory), The average execution time for each yield is:

1. 10-threads concurrency:

Number of yields	100	1000	10000	100000
Native thread	1201ns	633ns	640ns	632ns
UMS	2752ns	400ns	148ns	118ns
Fiber	96ns	105ns	101ns	88ns

2. 100-threads concurrency:

Number of yields	100	1000	10000	100000
Native thread	769ns	610ns	601ns	591ns
UMS	1428ns	245ns	152ns	128ns
Fiber	130ns	105ns	102ns	102ns

3. 1000-threads concurrency:

Number of yields	100	1000	10000	100000
Native thread	941ns	790ns	793ns	785ns
UMS	1400ns	276ns	146ns	127ns
Fiber	175ns	167ns	177ns	180ns

Notes

Some of the code is adopted from pervognsen's gist.