Date: Mon, 11 May 2015 11:48:21 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Andy Lutomirski <luto@kernel.org>
Cc: Len Brown <len.brown@intel.com>, Peter Zijlstra <peterz@infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Paul Mackerras <paulus@samba.org>, Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>
Subject: Re: [RFC] x86, perf: Add an aperfmperf driver
Message-ID: <20150511094821.GA7027@gmail.com>
References: <2c37309d20afadf88ad4a82cf0ce02b9152801e2.1430256154.git.luto@kernel.org>
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* 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
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