I/OAT ... Coming Soon ?

Andre Oppermann andre at freebsd.org
Thu Nov 15 16:22:13 PST 2007

Scott Ullrich wrote:
> On 11/15/07, Doug Ambrisko <ambrisko at ambrisko.com> wrote:
>> Hmm, I forgot about the 2970 which are AMD based.  Can you check the
>> BIOS to see if there is an option to turn it on?  I think this is an
>> Intel feature.  AMD might have something close?  We have one 2970
>> that we've played with a little but not much.  I can't say for sure
>> if it has it.
> Right you are.   As of BIOS 1.2.2 I do not see a I/OAT option.   Guess
> I will need to pick up a different server as we are interested in what
> kind of packet forwarding rate increase that this feature might bring
> on a heavily loaded firewall.

Not much.  Unless your firewall is in usermode.  Otherwise the data
stays in the kernel and I/OAT is of not help as no copying happens.
Your CPU is probably spending half of its clock cycles waiting on
cache misses from newly arrived packets.  Some Intel chipset integrated
gige ports have a cache prefetch feature (duno whether our driver
supports it) that would help quite a bit for your case.


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