From owner-freebsd-current  Wed Jun  4 00:31:45 1997
Return-Path: <owner-current>
Received: (from root@localhost)
          by hub.freebsd.org (8.8.5/8.8.5) id AAA01566
          for current-outgoing; Wed, 4 Jun 1997 00:31:45 -0700 (PDT)
Received: from user2.inficad.com (straka@user2.inficad.com [207.19.74.4])
          by hub.freebsd.org (8.8.5/8.8.5) with ESMTP id AAA01558
          for <current@freebsd.org>; Wed, 4 Jun 1997 00:31:43 -0700 (PDT)
Received: from localhost (straka@localhost) by user2.inficad.com (8.8.5/8.7.3) with SMTP id AAA15660 for <current@freebsd.org>; Wed, 4 Jun 1997 00:31:54 -0700 (MST)
Date: Wed, 4 Jun 1997 00:31:54 -0700 (MST)
From: Richard Straka <straka@inficad.com>
To: current@freebsd.org
Subject: sio driver performance
Message-ID: <Pine.BSI.3.95.970604001520.15234B-100000@user2.inficad.com>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
Sender: owner-current@freebsd.org
X-Loop: FreeBSD.org
Precedence: bulk

I have 2 16550A UARTS in a 486DX-33.  During probing, the sio
driver properly identifies both ports as 16550A's.

When sending sustained 115200 baud data from this machine, systat
(with vmstat option) indicates an interrupt rate of about 720/sec
with about 2% of the processor servicing interrupts.
When receiving sustained 115200 baud data, an interrupt rate of 
over 26,000/sec is indicated with about 15% of the processor going 
to service interrupts.

It appears as though the fifo is not working for the receive. In an
attempt to exhonerate the hardware, I swapped in another 16550 card
I had laying around and got the similar results.

Any help on this issue would be greatly appreciated. 

Richard Straka
straka@inficad.com