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Tweaked the siointr1() so that it works better at 921600 bps, especially

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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%.
This commit is contained in:
Bruce Evans 2003-11-17 07:21:19 +00:00
parent 170f850343
commit c0952034c3
1 changed files with 5 additions and 0 deletions
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5
sys/dev/sio/sio.c
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@ -1868,6 +1868,10 @@ if (com->iptr - com->ibuf == 8)
CE_RECORD(com, CE_OVERRUN); CE_RECORD(com, CE_OVERRUN);
} }
cont: 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 * "& 0x7F" is to avoid the gcc-1.40 generating a slow
* jump from the top of the loop to here * 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? */ /* output queued and everything ready? */
if (line_status & LSR_TXRDY if (line_status & LSR_TXRDY
&& com->state >= (CS_BUSY | CS_TTGO | CS_ODEVREADY)) { && com->state >= (CS_BUSY | CS_TTGO | CS_ODEVREADY)) {