-----Original Message----- From: Marc Jones [mailto:marc.jones@amd.com] Sent: Thursday, July 17, 2008 4:28 PM To: Myles Watson Cc: 'Coreboot' Subject: Re: [coreboot] HT credits and the Opteron
Myles Watson wrote:
Anyone with detailed knowledge of (or more manuals than I have for) the Opteron,
I just noticed that the Nvidia ck804 reduces the amount of credits which
the
Opteron gives it (probably due to an errata.) Does that mean that there should be more credits available for the other HT links? Is buffer
space
per link or does the CPU share it all between all the links? What if a
link
is disabled? Should you give its credits to the others?
In the BKDG for the Opteron it says that you shouldn't change the values
in
general, because software picks the right values, but that's us. It
doesn't
say how you should pick new values.
Myles,
Marc,
Thanks for the quick response.
I assume that you are talking about the XBAR buffer allocation, 4.6.12?
Sorry. I should have been more clear. I was talking about 3.3.15: LDTi Buffer Count Registers. Does your answer still apply?
The links are profiled by the designers and then appropriate values are assigned. There are some limitations in allocating the buffers so you can't just take some form one place an use it somewhere else. For the most part, you shouldn't run out of buffers in a typical system, so nothing would be gained by adding more to a particular interface.
Generally, we should set what the factory bios sets since those settings are validated. If a customer is building their own platforms we will work with them to set appropriate values for their silicon.
Now that there is an open-source HT core from the University of Mannheim, anyone could do this, but maybe most people will leave it alone.
Thanks, Myles