[ixp1200] Control of microengines and threads++

[Johnson, Erik J]

Going strictly from memory, here is what I remember 

1) How are the microACEs distributed among the microengines when using a
default configuration file? I am unable to find any documentation on
this subject (The ixsys.* files are generally poorly documented :)).

The distribution is based on the number, speed, and direction of the
interfaces.  For each 100Mb/s interface, two microengines are allocated
for all microblocks marked as "receive side", and one microengine is
allocated for all "transmit side" microblocks.  For every 4 10Mb/s
interfaces, one microengine is allocate for the receive side and one
microengine for the transmit side.

2) How can I control this distribution? Can I give any directives in the
configuration file to load an ACE on two engines, or is this done
programatically, i.e., when initializing the ace from the core?

Again from memory, if you use the ixsys config utility unmodified, then
I believe you are limited to the above distributions.  However, the
ixsys config is simply a utility built on top of the resource manager
APIs, so it is possible to write your own ixsys config utility (or
modify the existing one) to perform your own custom mapping.

3) How about the number of threads running on the engine? What is the
default and how can I control it?

The control of the threads per-microengine is embedded in the source
code itself.  That is, both the resource manager and the ixsys config
utility simply load the microengine with a single image and start all
threads executing.  That said, if you, for example, configured fewer
than 4 10Mb/s ports on the receive side microengine, the ingress ACE
code would likely kill the execution of some of the threads (however, it
has been a very long time since I looked at this code so if this is
critical to you, be sure to read the code).

4) Does the IngressACE do any processing of packets, or does it only
define the macros that I use in my dispatch loop? According to the
design documents and the source the latter seems to be it, but I'd like
to be 100% sure.

I guess it depends on your definition of "processing".  The ingress ACE
core component does not process packets.  The ingress ACE microblock
reassembles mpackets into a single packet and checks the destination MAC
address of the packet to ensure the packet belongs to the system.

5) Does anyone know how many cycles it takes the egress to transfer a
1024 byte large packet from SDRAM to the link? :) -Or where can I find
information about how the egress really works?

I don't know the transfer time.  As a shameless plug, if you want to
read about transmit on the IXP1200 you could check out the "IXP1200
Programming" book, Chapter 9.

erik

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Erik J. Johnson
Intel Research & Development
erik.j.johnson at intel.com
NOT SPEAKING FOR INTEL
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~