Subject: Re: DECchip 21143 and the tlp driver.
To: Wolfgang Rupprecht <firstname.lastname@example.org>
From: Thor Lancelot Simon <email@example.com>
Date: 10/30/1999 02:31:19
On Fri, Oct 29, 1999 at 02:38:50PM -0700, Wolfgang Rupprecht wrote:
> > I tried the above, but it didn't seem to matter. No amount of ifconfiging
> > can cause the media type to change.
> I just went to the console of my DFE-570TX machine and tried the
> ifconfig. I can confirm that the adaptor itself stays in the
> 100baseTX mode while the kernel thinks it is now 10baseT.
> Ping to a 10baseT host:
> 16008 bytes from 22.214.171.124: icmp_seq=0 ttl=0 time=29.370 ms
> Ping to a 100baseTX host:
> 16008 bytes from 126.96.36.199: icmp_seq=0 ttl=0 time=3.858 ms
> Since the pings to the 100baseTX host are ~10x faster, it looks like
> the interface is still speaking 100BaseTX. Interesting.
> > The fifo changes start to occure around the time that the quotas are being
> > checked. The machine in question has 3 scsi busses on it, and a couple of
> > them would be active checking the quotas. It appears that any amount of
> > traffic at this time causes the fifos to adjust.
> I can believe that 3 scsi buses would chew up all of one's PCI bandwidth.
> I wonder if there is any pci bus coupler tweaking that can be done by
> software to allow devices to get on and off the bus a bit faster.
Yeah, there is. Ironically, you need to do the reverse of what I
needed to do to my b0rken motherboard.
Make the PCI latency timer for the cards that are hogging the bus lower;
that will force them to relinquish the bus after N cycles. Some of the
SCSI drivers in the tree set the card's latency timer to 64 or 128
cycles, which is great for bandwidth but not so great for other cards'
ability to grab the bus when they want it! It's not clear to me that
any device drivers should really be doing this without being told to,
but it's easy enough to use one of them as an example of how to tweak
the value _down_ a bit. Try 32 or so, and see if that helps.
Also, some x86 machines' BIOS allows the default latency for all cards
to be set on one of the configuration screens. Maybe your machine has
it set really high, like 256 or something. Worth checking, anyway.
A nice trick to see how your PCI cards are set up, BTW, is to run
the "scanpci" program from XFree. Easier than monkeying with the
kernel, anyway... :-)
Thor Lancelot Simon firstname.lastname@example.org
"And where do all these highways go, now that we are free?"