Re: 2.5 or 2.4 kernel profiling

At 09:26 AM 12/12/00 -0600, Brian Ford wrote:

On Tue, 12 Dec 2000, Graham Stoney wrote:

quoted

Also, doesn't the 8260 have seperate memory subsystems to help get
around this?

I assume you are referring to the local bus?  Well yes, but there are
large
tradeoffs.

If you use the local bus for the receive buffers then you can have
simultaneous CPM to local bus and CPU to 60x bus transactions.  The catch
is that the local bus can not be cached.  So, you trade off bus contention
for caching/bursting.  The CPU must go across the 60x to local bus bridge
for those transactions.  The DMA engine can burst between the 60x and
local busses.

If the data has to end up in user space, it ends up being about a
wash, given the checksum and user space copy.  I need more testing to
confirm this, though.  If the user space copy was not needed, like for
routing, then it might help some.

--
Brian Ford
Software Engineer
Vital Visual Simulation Systems
FlightSafety International
Phone: 314-551-8460
Fax:   314-551-8444

I've been known to be wrong in the past, and I could be missing an
assumption, but local bus memory is cachable, it just isn't
snoopable.  If you need snooping as a prerequisite for enabling cache,
that would make the local bus effectively uncachable.  It also is 32
bits wide (max) rather than 64 which will affect your bus bandwidth.

gvb


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