usb: device_next: class: cdc_acm: throughput improvements (low hanging fruit) #99838
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Do not artificially limit the size of the USB request to the endpoint size, as this introduces multiple round trips through the CDC ACM class implementation. The USB stack handles packetizing to the maximum endpoint size. The maximum allocation size is limited to prevent starving other USB users. Throughput testing on a nRF52840DK with `CONFIG_UDC_BUF_POOL_SIZE=1024` shows a throughput increase from ~1.7 Mbps to ~2.7 Mbps. Signed-off-by: Jordan Yates <jordan@embeint.com>
When a custom pool is used for CDC ACM, allow the buffer sizes to be configured in Kconfig. Signed-off-by: Jordan Yates <jordan@embeint.com>
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Do not artificially limit the size of the USB request to the endpoint size, as this forces multiple round trips through the CDC ACM class implementation when the TX FIFO is larger than the endpoint size. The USB stack handles packetizing to the maximum endpoint size. The maximum allocation size is limited to prevent starving other USB users.
When a custom pool is used for CDC ACM, allow the buffer sizes to be configured in Kconfig.
Throughput testing on a nRF52840DK with
CONFIG_UDC_BUF_POOL_SIZE=1024shows a throughput increase from ~1.7 Mbps to ~2.7 Mbps.Steps towards improving the issue of #99779, but this is only the absolute lowest hanging fruit).
Throughput tested on the reproducer steps from the linked issue.
The limit of
CONFIG_UDC_BUF_POOL_SIZE / 4was picked out of thin air as a reasonable default, happy to hear arguments against.