0759386405
Previously rl(4) continuously checked whether there are RX events or TX completions in forever loop. This caused TX starvation under high RX load as well as consuming too much CPU cycles in the interrupt handler. If interrupt was shared with other devices which may be always true due to USB devices in these days, rl(4) also tried to process the interrupt. This means polling(4) was the only way to mitigate the these issues. To address these issues, rl(4) now disables interrupts when it knows the interrupt is ours and limit the number of iteration of the loop to 16. The interrupt would be enabled again before exiting interrupt handler if the driver is still running. Because RX buffer is 64KB in size, the number of iterations in the loop has nothing to do with number of RX packets being processed. This change ensures sending TX frames under high RX load. RX handler drops a driver lock to pass received frames to upper stack such that there is a window that user can down the interface. So rl(4) now checks whether driver is still running before serving RX or TX completion in the loop. While I'm here, exit interrupt handler when driver initialized controller. With this change, now rl(4) can send frames under high RX load even though the TX performance is still not good(rl(4) controllers can't queue more than 4 frames at a time so low TX performance was one of design issue of rl(4) controllers). It's much better than previous TX starvation and you should not notice RX performance drop with this change. Controller still shows poor performance under high network load but for many cases it's now usable without resorting to polling(4). MFC after: 2 weeks
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