Fedora SMP dual core, dual AMD 64 processor system

[Bryan J. Smith]

On Sat, 2005-09-24 at 16:38 -0400, Mark Hahn wrote:
> sure, but so what?  so SW raid will need to transfer a few extra 
> chunks over some of the 8GB/s HT channels, among some of the 
> 26 GB/s of memory bandwidth available.

I didn't know Opterons could distribute the I/O operations across CPUs
to use all that memory bandwidth.  You're throwing around theoretical
and aggregate maximums like that's actually what you're going to get.

> why do you think that a few hundred MB/s out of many GB/s is going
> to make a difference?

Yes, when you're moving those MBs through the CPU and turning it all
into one huge Programmed I/O (PIO) operation.  You're not going to get
GBps in transfers.  You're losing valuable chunks of time and,
therefore, cutting cycles away from transfer time as well.

Again, if it takes up 50% of your cycles just to push hundreds of MBs
data through the CPU, then you have reduced all that theoretical
bandwidth significantly.

> how strange!  what on earth do you think you can do with disks
> at 4 GB/s?  or are you worried about streaming reads from ~50
> disks at once?

But you're not getting 4GBps.  At this point, I need to bow out of this
discussion.  It's obvious that you believe you can push 8GB of data
through your CPU in a second.


-- 
Bryan J. Smith     b.j.smith at ieee.org     http://thebs413.blogspot.com
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