aglew@crhc.uiuc.edu (Andy Glew) (10/06/90)
Several questions about the Alliant, particularly the CCU/CCB
(concurrency control unit/bus). This is background information for a
paper. Please email replies to me at a-glew@uiuc.edu.
(1) In the FX/8 and FX/80, in what ways can the computational cluster be sliced,
ie. partitioned between different parallel programs?
As I recall, originally the 8 CE cluster could only be scheduled all
8 processors to the same job.
Then, I believe, Alliant announced that the cluster could be split
into 4+1+1+1+1 --- ie. one job could occupy 4 CEs, and the remaining
CEs could be scheduled to individual single CE jobs.
Is it possible to share the cluster between two parallel jobs, instead
of between one parallel and several non-parallel jobs. Eg. can 2 4 CE jobs
run on the cluster at the same time?
(1a) Is there any magic in the number 4 above? Or can you schedule jobs that require,
say, 2,3,5,6, or 7 processors - 6+1+1, and so on.
(2) [Hardware/architectural question]:
If 4+1+1+1+1 is the only type of partitioning of the cluster,
I hypothesize that it is because there is a single bit per CE,
controlled by the OS, that controls access to the CCB
(eg. if the bit is 0, then a program cannot write to the CCB,
and therefore cannot mess up other parallel programs from other users.
The OS must set the bit to 1 in order to use the CCB).
Is this the case?
But this would imply that 6+1+1 partitioning of the cluster were possible. Is it?
Although I suppose that the OS might have had an easy time if it only had to deal
with three job sizes (1,4, and 8 CEs).
(2a) If the cluster can be shared between two parallel jobs, how is access
to the CCB regulated, to prevent user programs from interfering with each other?
(3) My understanding is that the FX/800 is based on the i860,
and does not have a Concurrency Control Bus, although
it does implement the Concurrency Control instructions.
Is this correct?
Any help appreciated. Any pointers to available detailed technical
documentation on the Alliant systems (not marketing glossies) that do
not require purchase of a machine of a non-disclosure agreement would
be appreciated.
--
Andy Glew, a-glew@uiuc.edu [get ph nameserver from uxc.cso.uiuc.edu:net/qi]