HP OpenVMS Systems

Hints on Granularity Hints?

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The Question is:

 
Hi,
 
Please could you give me more information on the granularity hint regions
(or  tell me where I can find some). OVMS 7.1 Linker manual gives very brief
and in my oppinion unsufficient information on this issue.
 
Thank you,
Mihai
 
 

The Answer is :

 
  The Granularity Hints in the Alpha page table entries (PTEs) allow a
  single translation buffer (TLB) entry to describe a collection of 8,
  64, or 512 contiguous physical memory pages.
 
  This Alpha architectural feature is intended to serve the following
  functions:
 
    - efficient mapping of large and physically-contiguous system
      hardware structures, such as frame buffers.
 
    - efficient mapping of large and physically-contiguous software
      data structures, such as operating system code and data.
 
  The associated OpenVMS system parameters include GH_RES_DATA and
  GH_RSRVPGCNT.
 
  Global and Private sections can also get granularity hints by adding
  the flag SEC$M_GRANHINT.  One or more granularity hint regions will be
  created to map the section, depending on the alignment and size of the
  region to be mapped.  If SEC$M_EXPREG is used, CRMPSC will try to use
  the best alignment for the region.
 
  Granularity hint regions come in various sizes, and must be aligned on
  boundries that are a function of the region size.  Using EXPREG and
  GRANHINT minimizes the need for users to know the mechanics of the
  alignment and size rules.
 
  Minimizing TLB entries can have a significant benefit on performance,
  especially for large reqions with random or "sparse" access.
 
  For additional information on the Granularity Hints Region (GHR) and
  the (potentially beneficial) implications on the number of translation
  buffer misses, please see the system manager's manual.  For specific
  information on the implementation details of Granularity Hints, please
  see the Alpha Architecture Reference Manual.
 

  

     

     
answer written or last revised on ( 7-JUL-1999 )
     
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