[PATCH V2 3/6] stm class: provision for statically assigned masterIDs

[Mathieu Poirier]

On 8 February 2016 at 10:44, Al Grant <Al.Grant at arm.com> wrote:
>> Mike did write "master IDs are hardwired to individual cores and core security
>> states", which make assignment for one platform very static.
>> On the flip side those will change from one system to another.
>
> It depends on your perspective.  From the perspective of a userspace
> process not pinned to a core, the master id will appear to vary
> dynamically and unpredictably as the thread migrates from one
> core to another.  (That's actually useful if the decoder wants to know
> where the thread is running at any given point, as it can find that out
> for free, without the need to track migration events.)

Right, that's the expected (and desired) behaviour.

>
> On the other hand if you are pinned (e.g. you're the kernel on a
> particular core, or you're a per-core worker thread in some thread
> pooling system) then you have a fixed master id, and then you can
> have one instance per core all using the same range of channel
> numbers, with the master id indicating the core - this saves on
> channel space compared to having to give each core its own
> range of channel space.

>From an STM core and driver point of view channel mapping works the
same way - pinning of tasks is  a kernel artefact.  The problem of
representing masterIDs in the STM core for an architecture with HW
assigned masterIDs is still unresolved.

>
> Al
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