rf sv64 - bit virtual address space - ALL 64 bits


just to comment.

in the sigHPC working group we will begin to think about a true 64 bit address space (at a minimum). meaning ALL  64 bits have a meaning.

at BSC we are working on such a system.

in the past,  an exascale of performance matched up with an Exabyte of  storage. (one for one).

 i was personally involved with many projects of this type. 

today,  subject to cost and power this metric may not be attainable,  perhaps.  (typical 30 Megwatts Max power)

in any case,  an exabyte of physical storage requires,  for a 60 bit physical address, a 48 bit PPN.  in the current definition of sv57 this can not be defined (for a continuous 48 but field).   but that is ok,  sv57 is sv57. (sv57k).

so,  going forward, some of the characteristics of a TBD sv64 would be

.a true 64 bit virtual address space (no sign extensions)
.support of a PCAS reference model (needed for efficient implementations of UPC and CHAPEL)
.a PPN of a least 48 bits,  but preferably, 52 bits (thus 52+12 =  64)
.a 32 bit ASID
.a more contemporary security model
.100,000’s of nodes (or more). 

be safe

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