Database Reference
In-Depth Information
user land
udp_queue_rev_
skh
Kernel
udp_sendmsg
udp layer
udp_push_
pending_frames
udp_rcv
ip_push_
pending_frames
ip_rcv_finisih
IP layer
ip_output
ip_rcv
qdisc_run
netif_rx
HW independant
Driver
device drivers
wire
Figure 9-3.
UDP function execution stack
Network system calls are executed in kernel mode. So, a large amount of network traffic can lead to higher CPU
usage in kernel mode. In RAC, a large amount of cache fusion traffic can lead to higher CPU usage in kernel mode.
RDS protocol
RDS protocol is a low-latency, low-resource usage protocol. In UDP and TCP protocol processing, data is copied from
user space to kernel space and sent downstream through the layers of network. In contrast, RDS protocol can send
buffers directly from user space, avoiding a copy operation. On the receiving side, a copy operation is also avoided by
buffering the data directly to user space buffers.
Figure
9-4
shows the flow of data with InfiniBand fabric in play. TCP and UDP packets can flow through
InfiniBand infrastructure employing an additional
IP-over-IB
processing layer. The RDS protocol bypasses IP layers
and sends the packets directly through Host Channel Adapter and then through the fabric. Due to reduction in
processing layers, RDS is designed to be a lower-resource-usage protocol.
