Date: Sun, 09 Jul 2000 20:52:16 +1000 From: Stephen McKay <mckay@thehub.com.au> To: Stefan Esser <se@freebsd.org> Cc: Stephen McKay <mckay@thehub.com.au>, Alan Edmonds <aedmonds@digitalconvergence.com>, Bill Paul <wpaul@freebsd.org>, Chris Wasser <cwasser@v-wave.com>, freebsd-stable@freebsd.org Subject: Re: Strangeness with 4.0-S Message-ID: <200007091052.UAA09724@dungeon.home> In-Reply-To: <20000708221341.B2104@StefanEsser.FreeBSD.org> from Stefan Esser at "Sat, 08 Jul 2000 22:13:41 %2B0200" References: <200007030749.RAA13446@dungeon.home> <20000704140131.A1734@StefanEsser.FreeBSD.org> <200007041411.AAA18590@dungeon.home> <20000708221341.B2104@StefanEsser.FreeBSD.org>
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On Saturday, 8th July 2000, Stefan Esser wrote:
>Oh, there are renegotiations after each overrun ???
>They should not be required at all. The Ethernet chip probably supports
>writing a new prefetch limit into the register while fully active ...
>I have looked at a number of Ethernet controller data sheets. There never
>was a warning that the chip must be quiescent when the "early send" limit
>is modified.
The code at the point that an underrun is detected is:
printf("dc%d: TX underrun -- ", sc->dc_unit);
if (DC_IS_DAVICOM(sc) || DC_IS_INTEL(sc))
dc_init(sc);
After that, it sets the new threshold, or store and forward mode. That
conditional (which resets the DE-500 style cards I own), looks deliberate
since it is so specific. Either that, or Bill was being conservative.
When I get a chance, I will experiment with removing it.
>Well, I'd rather have the driver changed to not require a re-negotiation
>of the transmission parameters.
I haven't read the data sheet yet (downloading now). Then we should know
what limitations we have to live with.
>But as long as this is not the case, store-and-forward will at least
>hide that there is a problem ;-)
It hides the problem very well for me. I really can't see the tiniest
of performance loss with store and forward. Maybe it's something that
only shows up on benchmarks.
Stephen.
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