[rescue] J90 on epay

[Dave McGuire]

On Saturday, March 1, 2003, at 05:53 PM, Kris Kirby wrote:
>>    For booting, the IOS SS5 (the "master" IOS if there's more than 
>> one)
>> keeps the J90 processor halted, squirts a kernel into their memory
>> along with a configuration file which contains details device
>> configuration and such, then starts the processor at the entry point 
>> of
>> the kernel.  It's a fascinating process.  It took James Sharp and I
>> days of work to reverse-engineer how the boot process works.
>
> Fascinating indeed. You say J90 processor as if it's a single entity; 
> from
> your other comments, I gather that its a massive pile of specially made
> SS5s.

   No...I'm sorry if I misled you.  The J90 processor (well, processors 
plural, there are four processors in a module) is a CMOS implementation 
of the Cray YMP architecture in about five chips.  The SS5s are 
subprocessors outside of the J90 CPU/memory cabinet which handle 
I/O...they're 6U VME64 boards.  The one "regular" (unmodified Sun 
hardware) SS5 is the OWS, or Operator's Work Station, which is for 
booting and maintenance.

   Cray supercomputers fall into two major categories...the PVP machines 
(Parallel Vector Processor, the ones I like) and the MPP machines 
(Massively Parallel Processor, still cool but not my favorite).  The 
PVP machines are the Cray-proprietary vector processor machines and the 
MPP machines are based on other people's non-vector processors...the 
CS6400 is SPARC-based, the T3D and T3E use lots and lots of Alpha 21164 
processors, etc.

>  So the way you boot a big super is by jump-starting it? Does it have
> to load the kernel(s) into the boards one at a time, or all at once?

   The "master" IOS SS5 loads the UNICOS kernel from the disk array into 
the J90s memory...the memory is shared across all the J90's processors. 
  It then kickstarts the first processor on the loaded UNICOS kernel 
image.  It boots, starts the other processors, then mounts filesystems, 
etc etc and eventually presents you with a login prompt on the console 
and answers telnet/rlogin connections.

            -Dave

--
Dave McGuire             "I've grown hair again, just
St. Petersburg, FL           for the occasion."       -Doc Shipley