dc9643853d
Chelsio's TCP offload engine supports direct DMA of received TCP payload into wired user buffers. This feature is known as Direct-Data Placement. However, to scale well the adapter needs to prepare buffers for DDP before data arrives. aio_read() is more amenable to this requirement than read() as applications often call read() only after data is available in the socket buffer. When DDP is enabled, TOE sockets use the recently added pru_aio_queue protocol hook to claim aio_read(2) requests instead of letting them use the default AIO socket logic. The DDP feature supports scheduling DMA to two buffers at a time so that the second buffer is ready for use after the first buffer is filled. The aio/DDP code optimizes the case of an application ping-ponging between two buffers (similar to the zero-copy bpf(4) code) by keeping the two most recently used AIO buffers wired. If a buffer is reused, the aio/DDP code is able to reuse the vm_page_t array as well as page pod mappings (a kind of MMU mapping the Chelsio NIC uses to describe user buffers). The generation of the vmspace of the calling process is used in conjunction with the user buffer's address and length to determine if a user buffer matches a previously used buffer. If an application queues a buffer for AIO that does not match a previously used buffer then the least recently used buffer is unwired before the new buffer is wired. This ensures that no more than two user buffers per socket are ever wired. Note that this feature is best suited to applications sending a steady stream of data vs short bursts of traffic. Discussed with: np Relnotes: yes Sponsored by: Chelsio Communications |
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| .. | ||
| t4_connect.c | ||
| t4_cpl_io.c | ||
| t4_ddp.c | ||
| t4_listen.c | ||
| t4_tom_l2t.c | ||
| t4_tom_l2t.h | ||
| t4_tom.c | ||
| t4_tom.h | ||