From owner-freebsd-stable  Mon Apr 24 12:42:39 2000
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Message-ID: <003801bfae25$39a6d100$a44b8486@jking>
From: "Jim King" <king@sstar.com>
To: <e-masson@kisoft-services.com>, <freebsd-stable@FreeBSD.ORG>
References: <5564.000424@pd.chel.ru><20000424114057.A692@pir.net> <14596.37283.563515.214828@localhost.nantes.kisoft-services.com>
Subject: Re: sio interrupt handler problem
Date: Mon, 24 Apr 2000 14:42:09 -0500
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On Monday, April 24, 2000 1:25 PM, Eric Masson wrote:
> Peter Radcliffe writes:
> >Get some real serial ports.
> >
> >16450 ports, in my experience, really suck.  From the era when they
> >were common you can find dual fast serial cards with two 16550A ports
> >on them, which are considerably better.
> Hello
>
> Thinkpad 390 2626-700 (PII-266 64Mo)
>
> FreeBSD notbsdems.nantes.kisoft-services.com 4.0-STABLE
> FreeBSD 4.0-STABLE #0: Mon Apr 24 13:02:58 CEST 2000
> emss@notbsdems.nantes.kisoft-services.com:
> /usr/src/sys/compile/THINKPAD  i386
>
> sio0 at port 0x3f8-0x3ff irq 4 flags 0x10 on isa0
> sio0: type 16550A
>
> So i assume my box has real serial ports :).
>
> I encounter lots of silo overflows while using userland ppp under Xfree.
> - Under XFree86 4.0, approximately 250 Silo Overflows (SO) while fetching
> mail & news (10 minutes).
> - Under XFree86 3.3.6, approximately 220 SO for the same task.
> - Shell mode, xemacs -nw & fetchnews generate 1 SO from time to time.
>
> >From the previous, i could think that XFree86 is responsible for the SO,
> but one month ago this box was running 3.4-STABLE & XFree86 3.3.6 and I
was
> wondering what were these SO messages in freebsd-stable mailing list ;).
>
> I don't really understand the point. Maybe i misconfigured my kernel. Well
> all comments welcome.

One thing I've done in the past to overcome serial port problems is to patch
sys/isa/sio.c to set the FIFO receive trigger level to 8 bytes instead of 14
(FIFO_RX_MEDH instead of FIFO_RX_HIGH).  If you have a piece of hardware or
a misbehaved driver that's causing high interrupt latency this change be
really beneficial, and greatly outweighs the higher interrupt overhead when
using an 8 byte trigger.

<soapbox>
An 8 byte trigger is a safer option that causes better operation on weird
hardware without signifcantly changing anything on good hardware.  I really
wish sio.c would be changed to set the trigger to 8 bytes by default, or at
least have a flags option to change the trigger level.
</soapbox>

Jim




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