From c0952034c3cd5058ac188c365b1237d9ec37bdc4 Mon Sep 17 00:00:00 2001 From: Bruce Evans Date: Mon, 17 Nov 2003 07:21:19 +0000 Subject: [PATCH] Tweaked the siointr1() so that it works better at 921600 bps, especially 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%. --- sys/dev/sio/sio.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/sys/dev/sio/sio.c b/sys/dev/sio/sio.c index 42c285b9af71..1e06b59fdc69 100644 --- a/sys/dev/sio/sio.c +++ b/sys/dev/sio/sio.c @@ -1868,6 +1868,10 @@ if (com->iptr - com->ibuf == 8) CE_RECORD(com, CE_OVERRUN); } cont: + if (line_status & LSR_TXRDY + && com->state >= (CS_BUSY | CS_TTGO | CS_ODEVREADY)) + goto txrdy; + /* * "& 0x7F" is to avoid the gcc-1.40 generating a slow * jump from the top of the loop to here @@ -1905,6 +1909,7 @@ if (com->iptr - com->ibuf == 8) } } +txrdy: /* output queued and everything ready? */ if (line_status & LSR_TXRDY && com->state >= (CS_BUSY | CS_TTGO | CS_ODEVREADY)) {