Re: [PATCH V2 1/6] perf,core: allow invalid context events to be part of sw/hw groups

[Mark Rutland]

> Even if you ignore the fundamental semantics of groups, there are other
> problems with allowing shared contexts:
> 
> * The *_txn functions only get called on the group leader's PMU. If your
>   system PMU has these functions, they are not called.
> 
> * Event rotation is per ctx, but now you could have some events in a CPU
>   PMU's context, and some in the uncore PMU's context. So those can race
>   with each other.
> 
> * Throttling is also per-context. So those can race with each other too.

There's also a break down of behaviour: events in the uncore context
will get migrated to another CPU in the event of a hot unplug, while
events that are grouped with CPU events (and hence live in the CPU
context) will be destroyed.

Mark.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/