EC2 Graviton Windows 11 ARM ENA Network Performance Tested
Running Windows 11 ARM on a Graviton instance requires the AWS ENA ARM64 driver, which currently has only a single version (2.2.1). Can it saturate the t4g.large network burst limit? This article runs a complete iperf3 throughput test.
Test Environment
| Item | Configuration |
|---|---|
| Instance under test | t4g.large (2 vCPU / 8 GB), Windows 11 Pro 25H2 ARM64 |
| ENA Driver | AWS ENA ARM64 2.2.1.65 (ena.inf) |
| Link speed | 25 Gbps (reported by ENA) |
| Peer instance | t4g.medium, Amazon Linux 2023 aarch64 (same subnet) |
| Test tool | iperf3 3.21 (Windows x64 build, running under emulation) |
t4g.large network spec: Up to 5 Gbps (burst).
ENA ARM64 Driver Status
AWS provides ENA Windows drivers for two architectures:
- x64: Latest version 2.11.0 (2025-07), actively updated
- ARM64: Only 2.2.1.A (released 2024-05), no updates since
There is no upgrade path for the ARM64 driver. Do not attempt to install the x64 version — kernel drivers do not go through the emulation layer and will fail to load. 2.2.1.65 is the only available ARM64 version.
Test Results
TCP Throughput
| Scenario | Direction | Throughput | Retransmits |
|---|---|---|---|
| Single-stream TCP | Upload (Win → Linux) | 4.63 Gbps | — |
| 4 parallel streams | Upload (Win → Linux) | 4.72 Gbps | — |
| Single-stream TCP | Download (Linux → Win) | 3.61 Gbps | 0 |
| 4 parallel streams | Download (Linux → Win) | 3.78 Gbps | 1 |
UDP
| Scenario | Direction | Throughput | Packet Loss | Jitter |
|---|---|---|---|---|
| UDP 1G target | Upload | 378 Mbps | 0% | 0.081 ms |
| UDP 5G target | Upload | 385 Mbps | 0% | 0.066 ms |
Analysis
TCP upload near the limit: Single-stream reaches 4.63 Gbps and 4 parallel streams reach 4.72 Gbps — 92-94% of the t4g.large 5 Gbps burst limit. Hitting near-max with a single stream confirms TCP offload (checksum, segmentation) works correctly.
TCP download ~20% lower: The download direction hits 3.61-3.78 Gbps. Possible reasons include higher receive-path CPU overhead, the peer t4g.medium having a lower baseline, or ENA ARM64 2.2.1 having less mature RSS than newer x64 drivers. For real workloads, 3.6 Gbps receive is more than sufficient.
UDP limited by the test tool: UDP only reaching ~385 Mbps is not a driver issue. iperf3 runs under x64 emulation, and UDP sending is a pure user-mode operation (unlike TCP, which has kernel offload), so single-thread send performance is bounded by CPU + emulation overhead. Zero packet loss and very low jitter (0.066 ms) confirm the network path is clean.
Test Commands
Start iperf3 server on the Linux peer:
sudo dnf install -y iperf3
iperf3 -s -p 5201Run on the Windows instance under test:
# Single-stream upload (30 seconds)
iperf3.exe -c <server-ip> -p 5201 -t 30 -i 5
# 4 parallel streams upload
iperf3.exe -c <server-ip> -p 5201 -t 30 -i 5 -P 4
# Single-stream download (reverse mode)
iperf3.exe -c <server-ip> -p 5201 -t 30 -i 5 -R
# 4 parallel streams download
iperf3.exe -c <server-ip> -p 5201 -t 30 -i 5 -P 4 -R
# UDP tests
iperf3.exe -c <server-ip> -p 5201 -u -b 1G -t 30 -i 5
iperf3.exe -c <server-ip> -p 5201 -u -b 5G -t 30 -i 5Conclusion
ENA ARM64 driver 2.2.1.65 on Graviton2 + Windows 11 ARM:
- TCP upload: 4.63-4.72 Gbps, reaching 92-94% of the burst limit
- TCP download: 3.61-3.78 Gbps, sufficient for most workloads
- UDP: Zero packet loss, low jitter, excellent network quality
- Near-zero retransmits: Connection quality is excellent
Although the driver version is old (2.2.1, while x64 is at 2.11.0), it is not a bottleneck within the t4g.large network quota. If AWS releases a newer ARM64 ENA driver (more RSS queues, better interrupt coalescing), receive-direction performance may improve further.
Notes
- Burst vs baseline: t4g is a burstable instance. Sustained high-bandwidth transfers consume network burst credits. The 30-second test window keeps credits healthy; continuous traffic will drop to baseline (~0.5-1 Gbps).
- No ARM64 Windows iperf3 build exists: TCP offload happens in kernel mode, so emulation does not affect the TCP throughput conclusion. The UDP result, however, must be interpreted with the tool limitation in mind.
- Do not install the x64 ENA driver: Kernel drivers do not go through the emulation layer and will fail to load, leaving the instance unreachable.