Re: /proc/cpuinfo format - arch dependent!

["Bodo Eggert <harvested.in.lkml@posting.7eggert.dyndns.org>" <7eggert@gmx.de>]

Stefan Smietanowski <stesmi@stesmi.com> wrote:

>> I personally think that what would be useful is not "the number of CPUs"
>> (which does not make any sense), but an enumeration of :
>> 
>>     - the physical nodes (for NUMA)
>>     - the physical CPUs
>>     - each CPU's cores (for multi-core)
>>     - each core's siblings (for HT/SMT)
>> 
>> each of which would report their respective id for {set,get}_affinity().
>> This way, the application would be able to choose how it needs to spread
>> over available CPUs depending on its workload. But IMHO, this should
>> definitely not be put in cpuinfo. I consider that cpuinfo is for the human.
> 
> When one defines it one way you can be sure there'll come some company
> and figure something out that doesn't fit into that representation.
> 
> Like - Stick a board into the CPU slot of some motherboard. That board
> has two DualCore, SMT chips.

Obviously it must be a tree of CPU groups. CPUs in one NUMA node go into
one group, multi-core CPUs have all cores in one group and HT is a group,
too. This will scale from UP (degenerated tree with just one CPU) to
clusters with multicore HT-capable CPUs on PCI boards.

e.g. if you choose to represent it as a string:

Object            = <Offline-Indicator>? (<CPU>|<Group>) <Details>?
Offline-Indicator = "-"
CPU               = qr/[a-z0-9_]+/ # or more restrictive
Group             = "[" (<Object>)("," <Object>)* "]"
Details           = "{" (<vardef)("," <Vardef>)* "}"
Vardef            = <Key> "=" <Value> # or "=>" if you think perl
Key               = qr/[a-z0-9_]+/
Value             = qr/"([^"\000]|"")*"/

The described board in a UP system might look like:
[cpu0{speed="4.77MHz", RAM="80KB"},
 [[[boardcpu0_0, boardcpu0_0_ht]{group="ht"},
   [boardcpu0_1, boardcpu0_1_ht]{group="ht"}],
  [[boardcpu1_0, boardcpu1_0_ht]{group="ht"},
   [boardcpu1_1, boardcpu1_1_ht]{group="ht"}]{group="numa",RAM="4GB"}]

To count them, do:
#/usr/bin/perl
s/"[^"]*"//g;
s/\{[^}]*\}//g;
$numcpus=s/,/,/g + 1;
-- 
Top 100 things you don't want the sysadmin to say:
43. The backup procedure works fine, but the restore is tricky!

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