Re: [RFC] x86, perf: Add an aperfmperf driver

[Ingo Molnar <mingo@kernel.org>]

* Andy Lutomirski <luto@kernel.org> wrote:

> +	event->hw.idx = -1;
> +	event->hw.event_base = (event->attr.config == APERFMPERF_EVENT_APERF ?
> +				MSR_IA32_APERF : MSR_IA32_MPERF);

So instead of having a separate driver per MSR, I think it might be 
more useful to have a generic 'MSR as counters' PMU driver, for such 
really simple cases where MSR contents represent an interesting 
hardware metric, and have a table that enumerates the MSRs we allow to 
be measured, and a sysfs list of them, to allow easy discovery.

APERF/MPERF would be one such MSR, MSR_SMI_COUNT another one - but 
there are also other interesting ones.

Some of these are per CPU, some are system wide. Such an approach 
would be far more robust than tooling poking around in /dev/msr (!).

Thanks,

	Ingo