Xref: utzoo comp.dcom.modems:2708 comp.mail.uucp:2165
Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!wasatch!utah-gr!uplherc!sp7040!obie!wsccs!terry
From: terry@wsccs.UUCP (Every system needs one)
Newsgroups: comp.dcom.modems,comp.mail.uucp
Subject: Re: UUCP g stats
Message-ID: <728@wsccs.UUCP>
Date: 12 Oct 88 02:29:27 GMT
References: <183@arnold.UUCP> <1988Sep20.184054.2403@utzoo.uucp> <184@arnold.UUCP> <21254@watmath.waterloo.edu>
Lines: 43

In article <21254@watmath.waterloo.edu>, egisin@watmath.waterloo.edu (Eric Gisin) writes:
> In article <201@arnold.UUCP>, dave@arnold.UUCP (Dave Arnold) writes:
> > I am seeing the same 400-600 cps on a direct 9600 baud link between
> > a uVax and something else.  Can somebody out there tell me where the
> > bottleneck on the VAX is?
> 
> Lack of CPU power mostly.
> The BSD tty device drivers passes input characters one-at-a-time
> to the line drivers through the line switch l_rint (receiver interrupt)
> function.
> The expensive calling convention on the VAX makes things worse here.
> 
> A 785 won't handle trailblazer input either,
> it only gets 1100-1200 B/s on an idle system.
> It can easily do output at full speed to a more modern Unix box though.

The problem, Eric, is most likely the DHV-11 interrupt controller that the
uVAX comes with, not any inherent problems with the machine.  A DMA
controller will ease the problem greatly.

The BSD drivers only do this 1) if they are very badly written or 2) if
some idiot turns on CBREAK and sets the buffer size to 1 and demands
flushing.  Now... I'm not saying this is the case, but it seems to me
that if you were to block reads with either a timeout or a selectio and
read for GPACKSIZ characters, this problem wouldn't happen.

The "expensive calling convention" would only come into play if you were
dumb enough to use vcc.

While I am unsure as to 19200 baud (I have yet to get my grubby hands on
a 19200 baud board for the uVAX ;-), I do KNOW that our emulation/transfer
software CAN do 9600, so there is no inherent architecture faults.

As to inefficiency of interrupt controllers, that's bogus.  I have an interrupt
driver for an 8Mghz AT that will do 57K under DOS, and have had no problem with
19200 and an ocassional 38.4 on the same machine under Xenix.

| Terry Lambert           UUCP: ...{ decvax, ihnp4 } ...utah-cs!century!terry |
| @ Century Software        OR: ...utah-cs!uplherc!sp7040!obie!wsccs!terry    |
| SLC, Utah                                                                   |
|                   These opinions are not my companies, but if you find them |
|                   useful, send a $20.00 donation to Brisbane Australia...   |
|                   'I have an eight user poetic liscence' - me               |