Chelsio Communications Chelsio T5 Uživatelská příručka stáhnout pdf (Strana 85)

Chapter V. WD-UDP

Chelsio T5/T4 Unified Wire For Linux Page 85

4. Software/Driver Configuration and Fine-tuning

4.1. Accelerating UDP Socket communications

The libcxgb4_sock library is a LD_PRELOAD-able library that accelerates UDP Socket

communications transparently and without recompilation of the user application. This section

describes how to use libcxgb4_sock.

By preloading libcxgb4_sock, all sockets created by the application are intercepted and possibly

accelerated based on the user’s configuration. Once accelerated, data for the UDP endpoint are

transmitted or received via HW queues allocated specifically for the accelerated endpoint,

bypassing the kernel, the host networking stack and sockets framework, and enabling ultra-low

latency and high bandwidth utilization.

Due to HW resource limitations, only a small number of queues can be allocated for UDP

acceleration. Therefore only performance critical UDP applications should use libcxgb4_sock.

Only 64 IPv4 UDP sockets / 28 IPv6 UDP Sockets can be accelerated per Chelsio T5/T4

device used.

4.1.1. Application Requirements

Certain application behavior is not supported by libcxb4_sock in this release. If your application

does any of the following, it will not work with libcxgb4_sock:

Calling fork() after creating UDP sockets and using the UDP socket in the child process.

Using multiple threads on a single UDP socket without serialization. For instance, having

one thread sending concurrently with another thread receiving. If your application does this,

you need to serialize these paths with a spin or mutex lock.

Only 1 UDP endpoint is allowed to bind to a given port per host. So if you have multiple

processes on the same host binding to the same UDP port number, you cannot use

libcxgb4_sock.

Applications must have root privileges to use libcxgb4_sock.

Applications requiring bonded T5/T4 interfaces are not currently supported.

The performance benefit observed with libcxgb4_sock will vary based on your application’s

behavior. While all UDP IO is handled properly, only certain datagrams are accelerated. Non

accelerated IO is handled by libcxgb4_sock via the host networking stack seamlessly. Both

Unicast and Multicast datagrams can be accelerated, but the datagrams must meet the

following criteria:

Non fragmented. In other words, they fit in a single IP datagram that is <= the T5/T4 device

MTU.

Routed through the T5/T4 acceleration device. If the ingress datagram arrives via a device

other than the T5/T4 acceleration device, then it will not utilize the acceleration path. On

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