Re: Celistica with AMD chip-set

[Arthur Perry]

I believe that in the card's own PCI config space, there should be a
bit (bit 3) in the BAR configuration register which will tell "somebody" how to set up the device.
Bit 3 tells "somebody" whether or not it is prefetchable.
The bridge then be configured properly for this device.

I am not sure yet just who this should be, but my guess is that there should be a routine
in BIOS that does this.

So the first question I think is to verify that the card does indeed set this bit proper
for the BARs used.

If it is then not being set in the bridge, I would suspect a fault in BIOS.

Am I missing something here?
Please let me know if I am totally off track.


Thanks!




On Mon, 30 Aug 2004, Arthur Perry wrote:

> Hello Alan and Richard,
>
> I have to advise caution here, as it is currently unconfirmed whether or
> not the PCI bridge configuration is "incorrect", and that it has "very
> poor PCI performance".
> Unless everyone in the whole wide world is setting this value and we are
> the only ones who are not, I find it hard to believe that this statement
> is not overspeculative.
>
> The proper place for this should be in the BIOS, if it is indeed a true
> optimization point.
> But until that is positively identified, we should not assume that
> applying this globally for everyone is the right thing to do.
> As in any assumed optimization for a simgle case, it could potentially
> cause performance degradation in somebody else's HBA.
>
> This is a cache optimization.
>
> Have you considered the possibility of this "optimization" causing a
> performance hit with Mellanox's PCI implementation?
>
> What about people who have already tailored their device driver to work
> well in on this chipset and currently use "read multiple" rather than
> "read cacheline". This optimization could potentially cause a slight
> degradation of performance for them.
>
> I just propose that we test this change with various card vendors and see
> what the real impact is before we jump to the conclusion that this is a
> serious performance problem for everybody.
>
> Secondly, if it is the case, then the correct place to put this change is
> in the system's BIOS, and having a software workaround is a last resort.
>
> If you want, I can write a userspace utility to package with your existing
> tools that can be installed and launched from init to provide this
> optimization feature to the 8131 PCI bridge that your card resides on, to
> ensure that your card gets this necessary optimization.
> Or, you can easily put this capability into your existing device driver.
>
> I would just rather not assume too much when dealing with something that
> can potentially have a large reprocussion.
>
>
>
>
>
>
> On Mon, 30 Aug 2004, Alan Cox wrote:
>
> > On Llu, 2004-08-30 at 15:02, Richard B. Johnson wrote:
> > > Hello all,
> > >
> > > The Celistica server with the AMD chip-set has very poor
> > > PCI performance with Linux (and probably W$ too).
> > >
> > > The problem was traced to incorrect bridge configuration
> > > in the HyperTransport(tm) chips that connect up pairs
> > > of slots.
> >
> > Can you get Celestica to mail me their PCI subvendor
> > id/devid's for the problem configuration or DMI strings
> > and then we can do a PCI quirk properly for this.
> >
> > Alan
> >
> > -
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>
>
>
>
>
> Arthur Perry
> Linux Systems/Software Architect
> Lead Linux Engineer
> CSU Validation Group
> Celestica, Salem, NH
> aperry@xxxxxxxxxxxxx
>
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Arthur Perry
Linux Systems/Software Architect
Lead Linux Engineer
CSU Validation Group
Celestica, Salem, NH
aperry@xxxxxxxxxxxxx

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