4/30/2024 0 Comments Cs what does front of queue mean![]() ![]() ![]() For example, if an application writes 2,000 bytes to a TCP socket then the IP stack needs to create two IP packets to keep the packet size less than or equal to a 1,500 MTU. Inside IP network stack, the MTU can manifest as a limit on the size of the packets which are sent to the device for transmission. For Ethernet the default MTU is 1,500 bytes but some Ethernet networks support Jumbo Frames of up to 9,000 bytes. Most NICs have a fixed maximum transmission unit (MTU) which is the biggest frame which can be transmitted by the physical media. 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. 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. Figure 2 – Partially full driver queue with descriptors pointing to SKBs ![]()
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