c0952034c3
with multiple ports on a shared interrupt demultiplexed by the puc_intr() handler. siointr1() first read as much input as possible and then checked all possibly-relevant status registers, partly for robustness and partly for historical reasons. This is very bad if it is called for every port sharing an interrupt like puc_intr() does. It can spend too long reading all the input for some ports when the interrupt is for a more urgent event on another, or just too long checking all the status registers when there are lots of ports. The inter-character time is too long for reading all the input even when the interrupt is for a transmitter interrupt on the same port, and at 921600 bps the inter-char time is 10.85 usec and was often exceeded with just 2 ports, leaving the transmitters idle for about 6% of the time. The tweak is to break out of the read loop after reading 1 char if output can be done. This avoids most of the idle transmitter time for 2 active ports at 921600 bps bidirectional on the test system. It also reduces overhead by about 20%. More complete fixes use the programmable tx low watermark on 16950's and reduce overhead by another 65%. |
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| .. | ||
| sio_ebus.c | ||
| sio_isa.c | ||
| sio_pccard.c | ||
| sio_pci.c | ||
| sio_puc.c | ||
| sio.c | ||
| sioreg.h | ||
| siovar.h | ||