linux-kernel - Re: [RFC PATCH] perf: Provide status of known PMUs

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Message-ID: <20150709085022.GB2859@worktop.programming.kicks-ass.net>
Date:	Thu, 9 Jul 2015 10:50:22 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Vince Weaver <vincent.weaver@...ne.edu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-kernel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>,
	Stephane Eranian <eranian@...gle.com>,
	Borislav Petkov <bp@...e.de>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [RFC PATCH] perf: Provide status of known PMUs

On Thu, Jul 09, 2015 at 10:48:00AM +0300, Adrian Hunter wrote:
> Known PMUs may not be present for various reasons.
> Provide a way for the user to know what the reason
> is.

Not a bad idea, but I do wonder where we should draw the line on what is
'known'. The patch as proposed will have bts/pt listed as 'known' for
every arch out there.

By that logic, x86 should list the ppc/sparc/mips/arm/etc.. PMUs as
known and wrong_arch too, which might be a tad excessive.

Can we limit it to PMUs for which we've (attempted to) load the drivers?
That would obviously make a few of your status bits redundant, but then
you've not explained why we're interested in it.

> 	Supported
> 	Driver error
> 	Driver not loaded
> 	Not supported by hardware
> 	Wrong vendor
> 	Unknown status

There would work.

> 	Driver not in kernel config
> 	Not supported by kernel
> 	Wrong architecture

These will be hard, for if we don't load the driver we don't 'know' of
them.
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