Re: Differences between AMD and Intel CPUs [was: Re: Dragonfly andHyperthreading....]

[EM1897@xxxxxxx]

In a message dated 3/11/2005 12:25:47 PM Eastern Standard Time, Joerg Sonnenberger <joerg@xxxxxxxxxxxxxxxxx> writes:

>On Fri, Mar 11, 2005 at 08:37:17AM -0800, Boris Spirialitious wrote:
>> Yes, I agree here. We have FreeBSD machine that 
>> we get device timeouts and it running at very 
>> high usage using 2 intel nics on motherboard. 
>> We find out these are only running 33mhz and 
>> we put 2 port intel pcix card in machine. Now it 
>> run 30% all day. Everything else the same. pcix is
>> very good and important.
>
>I think that's a more the fault of Intel's memory architecture
>and not so much of PCI-X. Keep in mind that Intel doesn't use
>a point-to-point bus like AMD / DEC, so the CPU has to fight
>with the host-to-PCI bridge for the memory access. This is
>something which doesn't affect the CPU on AMD systems at all.

Why don't you just do some testing, Joerg, instead of
trying to reason yourself into thinking that you are
right? Do you have any evidence of your claim? A minute
ago you said PCI-X was irrelevant, now you have a 
different answer, none based on anything but conjecture. 
Why not try to find out the real answer, instead of 
spending all of your time trying to save face? If you 
never admit you are wrong, then you'll never get any
smarter.

How many I/O operations are there in an ethernet driver
to process say, 1000pps? 50k? 100k? The more the PCI
bus is saturated, the longer those operations take. A 
standard PCI bus is, realistically, fairly well saturated
with 2 devices passing 80Kbs. So those I/O operations may
have to wait 2 full dma bursts before they can get access
to the controller. With an 8Gb/s bus (pci-x), the operations
usually complete in one cycle, and they are faster also,
because 1) the bus is faster and wider and 2) the bus is 
almost always available. You add up all of those cycles 
and its a huge difference in cpu usage. And as the network
usage increases, the gains become even more pronounced.