Date: Thu, 12 Jun 2003 05:21:03 -0400 (EDT) From: Jeff Roberson <jroberson@chesapeake.net> To: arch@freebsd.org Subject: HyperThreading and CPU topologies. Message-ID: <20030612051553.J36168-100000@mail.chesapeake.net>
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While I was at USENIX I started implementing HTT support in ULE. To do
this I needed a way for the machine dependant code to tell the MI code
about the CPU topology. I decided to make this generic enough to handle
architectures more complicated than a few HTT capable cores.
What I came up with can be used to describe N tiers of CPU groups each
containing a variable number of processors. For the Hyper threading case
you make one level of groups that each have all of the logical cores for
one physical cpu in that group.
For something like NUMA you would have one group for each node and one
group for each CPU in that node. This is different from HTT where you
have one group for each physical cpu.
Below I'll supply the patch for sys/smp.h. One thing to note is that I
intend for the smp_topology to be optional. If it is not supplied strict
SMP will be assumed. That way MD code for all architectures doesn't have
to be updated. Just those who support HTT (Or some other SMT
implementation) or NUMA (hah).
Here's the structures:
Index: smp.h
===================================================================
RCS file: /home/ncvs/src/sys/sys/smp.h,v
retrieving revision 1.72
diff -r1.72 smp.h
19a20,46
>
> /*
> * Topology of a NUMA or HTT system.
> *
> * The top level topology is an array of pointers to groups. Each group
> * contains a bitmask of cpus in its group or subgroups. It may also
> * contain a pointer to an array of child groups.
> *
> * The bitmasks at non leaf groups may be used by consumers who support
> * a smaller depth than the hardware provides.
> *
> * The topology may be omitted by systems where all CPUs are equal.
> */
>
> struct cpu_group {
> int cg_mask; /* Mask of cpus in this group. */
> int cg_count; /* Count of cpus in this group. */
> int cg_children; /* Number of children groups. */
> struct cpu_group **cg_child; /* Optional child group. */
> };
>
> struct cpu_top {
> int ct_count; /* Count of groups. */
> struct cpu_group **ct_group; /* Array of pointers to cpu
groups. */
> };
>
> extern struct cpu_top *smp_topology;
Cheers,
Jeff
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