Subject: Re: silo overflows, was fifo overruns
To: Jason Thorpe <>
From: James Graham - Systems Mangler <>
List: current-users
Date: 11/12/1997 19:37:46
Hiya, Jason!
Jason Thorpe sez:
 *  > Ah, yes, but what kind of serial I/O did it have?  Certainly not the
 *  > zs8530 which, while supporting two serial ports, only has a two-and-a-
 *  > half byte Hardware FIFO for each port (two bytes of FIFO and a third
 *  > to hold the one that's coming in).
 * Um, all SPARCs have 8530-based serial ports.

Well, yes, but he was talking about Macs, which I now understand have
the same hardware.

I think we've been this go-round before, with input from Chris Torek
[Hiya, Chris! :-)] suggesting the very same thing that's "coming to
light" now, i.e., that the interrupts are not being serviced quickly

I believe the change in performance came during the major MD->MI migration
which was, IIRC, sometime around 1.2C[?] which was [IIRC] October/November/
December 199_6_.

I'm completely baffled as to why only now we're getting around to
discussing it when it's been a problem for the last year.

[Damn -- can't seem to stop the initially self-referential paragraphs.
Sorry; I'm not an egotist, really!]

One thing I _did_ discover was that upping splzs from 12 to 14 most
certainly does NOT affect the problem.  Something else is just holding
onto a high-level interrupt.

Putting two and two together, I wonder if it's the statclock, since I
seem to remember something about 'vmstat/pstat finally working right'
at just about the same time the serial ports "broke" -- is there
something in that, or am I seeing smoke here?


A whole wide world, an endless universe/Yet we keep looking thru the eyeglass
in reverse/Don't feed the people but we feed the machines/Can't really feel
what "international" means/In different circles we keep holding our ground/
Indifferent circles we keep spinning round and round and round//
	- Rush:/Power_Windows/Territories