On Wed, Feb 01, 2023 at 04:56:17PM -0800, Justin Muir wrote:
> As requested, dmesg output:
...
> cpu0: smt 0, core 0, package 0
> cpu1: smt 1, core 0, package 0
> cpu2: smt 0, core 1, package 0
> cpu3: smt 1, core 1, package 0
This CPU presents itself as two cores, each with two threads, making a total
of four.
As a result, OpenBSD will not schedule processes on the 'extra' threads.
Since the AMD bulldozer architecture, (which this CPU is based on), includes a
physical integer execution unit for each thread, it's possibly not as crippled
as most SMT CPUs. Depending on the mix of instructions in the code you are
running, you _might_ see a decent performance increase by enabling SMT on
OpenBSD.
You might also see a performance decrease, for example if you end up running
two floating point threads on the same physical core and leaving the other one
idle instead of running them on the separate physical cores.
As previously advised, enabling SMT on any CPU potentially facilitates a number
of attacks against the system, which have been widely discussed elsewhere.
Whether this is a concern for your particular usage scenario is a question
that only you can really answer.
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