Re: [PATCH] Use uname not sysctl to get the kernel revision

[Ulrich Drepper]

Eric W. Biederman wrote:
> Ulrich what would be interesting besides the possibility of having
> multiple cpus?

What is needed for various things like memory handling etc is all
topology information.  Somebody might remember the numa library proposal
I had in April 2004 which was cast aside because people were only
looking for a "quick fix".  Well, the problem still isn't solved.

IMO the vdso should export information about:

- processors and their relationship (hyperthreads, cores)

- the CPU caches and how they relate to the cores (e.g., dual core
  with shared L2)

- local main memory for each processor

- relative costs of the memory access of the various memory regions
  (for numa local memory to a node, intra-node costs)

- ideally, relative costs main memory and CPU caches


All this information can be steadily updated by the kernel as new
CPUs/memory get added/removed.  The vdso should have functions to access
this information.  It's easy enough to make this access race free.

I guess I should try to come up with a representation for this
knowledge.  Collecting the information (except the costs) should be
easy.  Determining the costs also shouldn't be that hard but it can be
very useful.  Some of this information could be determined at userlevel
but you really don't want every process to compute all this from
scratch.  And stored data in a file is stale if the system changes.

-- 
â Ulrich Drepper â Red Hat, Inc. â 444 Castro St â Mountain View, CA â

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