In the case of c# (NdisApiDemo), the CPU usage is high when the program is compi

[xiangenmin]

In the case of c# (NdisApiDemo), the CPU usage is high when the program is compiled and run

[xiangenmin]

private static unsafe void PassThruUnsortedThread
(
NdisApi filter,
WaitHandle[] waitHandles,
IReadOnlyList<AutoResetEvent> waitHandlesManualResetEvents)
{
const int bufferSize = 32;

var buffers = new IntPtr[bufferSize];
for (int i = 0; i < buffers.Length; i++)
{
buffers[i] = (IntPtr)filter.CreateIntermediateBuffer();
}

while (true)
{
WaitHandle.WaitAny(waitHandles);
uint packetsSuccess = 0;

while (filter.ReadPacketsUnsorted(buffers, bufferSize, ref packetsSuccess))
{
for (int i = 0; i < packetsSuccess; i++)
{
EthernetPacket ethPacket = buffers[i].GetEthernetPacket(filter);
if (ethPacket.PayloadPacket is IPv4Packet iPv4Packet)
{
if (iPv4Packet.PayloadPacket is TcpPacket tcpPacket)
{
//Console.WriteLine($”{iPv4Packet.SourceAddress}:{tcpPacket.SourcePort} -> {iPv4Packet.DestinationAddress}:{tcpPacket.DestinationPort}.”);
}
}
}

if (packetsSuccess > 0)
{
filter.SendPacketsUnsorted(buffers, packetsSuccess, out uint numPacketsSuccess);
}
}
}
}
}

 

The demo has high CPU usage

c# 调用驱动的时候，16核心cpu 占用16%

[Vadim Smirnov]

The high CPU usage is likely due to the fact that the packet event is never reset. This causes the thread to continuously poll the driver without pausing.

Solution:
You need to reset the AutoResetEvent or ManualResetEvent in waitHandlesManualResetEvents after processing packets. This ensures the thread properly waits for new packets instead of running in a tight loop.

Fixed Code:

private static unsafe void PassThruUnsortedThread
(
    NdisApi filter,
    WaitHandle[] waitHandles,
    IReadOnlyList<AutoResetEvent> waitHandlesManualResetEvents)
{
    const int bufferSize = 32;
    var buffers = new IntPtr[bufferSize];

    for (int i = 0; i < buffers.Length; i++)
    {
        buffers[i] = (IntPtr)filter.CreateIntermediateBuffer();
    }

    while (true)
    {
        int eventIndex = WaitHandle.WaitAny(waitHandles);  // Wait for an event to be signaled

        uint packetsSuccess = 0;

        while (filter.ReadPacketsUnsorted(buffers, bufferSize, ref packetsSuccess))
        {
            for (int i = 0; i < packetsSuccess; i++)
            {
                EthernetPacket ethPacket = buffers[i].GetEthernetPacket(filter);
                if (ethPacket.PayloadPacket is IPv4Packet iPv4Packet)
                {
                    if (iPv4Packet.PayloadPacket is TcpPacket tcpPacket)
                    {
                        // Console.WriteLine($”{iPv4Packet.SourceAddress}:{tcpPacket.SourcePort} -> {iPv4Packet.DestinationAddress}:{tcpPacket.DestinationPort}.”);
                    }
                }
            }

            if (packetsSuccess > 0)
            {
                filter.SendPacketsUnsorted(buffers, packetsSuccess, out uint numPacketsSuccess);
            }
        }

        // Reset the event to allow proper waiting
        if (eventIndex >= 0 && eventIndex < waitHandlesManualResetEvents.Count)
        {
            waitHandlesManualResetEvents[eventIndex].Reset();
        }
    }
}

Explanation:

• Wait for an event: WaitHandle.WaitAny(waitHandles); ensures the thread only runs when a packet event is signaled.
• Process packets normally: The loop reads packets, processes them, and sends them back.
• Reset the event: After processing packets, waitHandlesManualResetEvents[eventIndex].Reset(); is called to prevent continuous polling.

This should significantly reduce CPU usage.

[xiangenmin]

Thank you

if (eventIndex >= 0 && eventIndex < waitHandlesManualResetEvents.Count) { waitHandlesManualResetEvents[eventIndex].Reset(); }

 

waitHandlesManualResetEvents[eventIndex]

 

Array index out of bounds

此处代码会出现数组索引越界

[Vadim Smirnov]

Thank you for pointing that out. I made an incorrect assumption about the parameters, but I believe you understood the main idea correctly—when there are no packets to read, the packet events should be reset, and the thread should wait on them. I appreciate the clarification!

[Author]

Posts