This is also not ideal because the IP stack cannot move on to other work. The opposite approach would be for the IP stack to wait after a packet is created until the hardware is ready to transmit. Since responding to this request cannot be instantaneous this design wastes valuable transmission opportunities resulting in lower throughput. One alternative design would be for the NIC to ask the IP stack for data whenever the physical medium is ready to transmit.
Kernel stack size driver#
That is, the driver queue gives the IP stack a location to queue data asynchronously from the operation of the hardware. The reason the driver queue exists is to ensure that whenever the system has data to transmit, the data is available to the NIC for immediate transmission. Packets added to the driver queue by the IP stack are dequeued by the hardware driver and sent across a data bus to the NIC hardware for transmission. The packets may be generated locally or received on one NIC to be routed out another when the device is functioning as an IP router. The input source for the driver queue is the IP stack which queues complete IP packets.
Kernel stack size full#
Figure 2 – Partially full driver queue with descriptors pointing to SKBs Instead it consists of descriptors which point to other data structures called socket kernel buffers ( SKBs) which hold the packet data and are used throughout the kernel. The driver queue does not contain packet data.
This queue is typically implemented as a first-in, first-out (FIFO) ring buffer – just think of it as a fixed sized buffer. Figure 1 – Simplified high level overview of the queues on the transmit path of the Linux network stack Driver Queue (aka ring buffer)īetween the IP stack and the network interface controller (NIC) lies the driver queue. The figure below will be referenced throughout and modified versions presented to illustrate specific concepts.
Kernel stack size how to#
This article aims to explain where IP packets are queued in the Linux network stack, how interesting new latency reducing features such as BQL operate and how to control buffering for reduced latency. They allow for asynchronous modules to communicate, increase performance and have the side affect of impacting latency. Packet queues are a core component of any network stack or device.
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