Chapter 3: What's New; Queue Handling; Receive - Xilinx Alveo X3522 User Manual

What's New
The X3522 adapter has been engineered from scratch to provide absolute lowest latency. This
has resulted in differences in its hardware capabilities and host interface from its predecessors
that were designed by Solarflare, such as the 7000-series, 8000-series and XtremeScale X2-
series. This chapter describes those differences, and resultant changes in deployment to take
best advantage of them.
Note: Low-level changes that impact acceleration technologies such as Onload, TCPDirect and ef_vi are
described in the corresponding User Guide. See References.

Queue Handling

The key difference between the X3522 and its predecessors is its queue handling:
• Predecessors of the X3522 bundle together a receive queue, transmit queue, event queue,
and interrupt and call these a virtual interface (VI), They present a very large number (typically
1000s) of VIs that can be allocated to applications on demand.
• The X3522 has entirely separate receive and transmit queues that can be allocated more
flexibly. They can be directed to separate event queues, and the event queues can be shared.
The X3522 presents fewer queues (typically one per CPU, but with an overall limit) and
applications can attach to them as required.

Receive

On the receive side, because there are a reduced number of queues they will in some situations
need to be shared. The intended model is that a receive queue is associated with a CPU cluster
to benefit from cache locality, and all the applications running on that cluster share that queue.
Because the receive queues are shared they must be managed by the driver rather than directly
by the applications.
On predecessors to the X3522 such as the X2522, packets are received into a 4 KB standard
page:
• Applications own and manage the packet buffers, and post them to the NIC.
UG1523 (v1.0) October 18, 2022
Alveo X3522 User Guide

Chapter 3: What's New

Chapter 3
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