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

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Message-ID: <20150709081011.GA31953@gmail.com>
Date:	Thu, 9 Jul 2015 10:10:11 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Adrian Hunter <adrian.hunter@...el.com>
Cc:	Peter Zijlstra <peterz@...radead.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


* Adrian Hunter <adrian.hunter@...el.com> wrote:

> Known PMUs may not be present for various reasons.
> Provide a way for the user to know what the reason
> is.
> 
> A bus attribute is created for each known PMU beneath
> a group "known_pmus".  The attribute name is the same
> as the PMU name.  The value is a string consisting of
> one or, optionally, two parts: a canonical part, and
> a driver specific part.  If there are two parts, they
> are separated by " - ".  The canonical part is one of:
> 
> 	Supported
> 	Driver error
> 	Driver not loaded
> 	Driver not in kernel config
> 	Not supported by kernel
> 	Not supported by hardware
> 	Wrong vendor
> 	Wrong architecture
> 	Unknown status

Very nice!

> Example:
> 
> 	$ cat /sys/bus/event_source/known_pmus/intel_pt
> 	Supported

So I only have naming nits. 'Supported' is a bit ambiguous, because it could mean 
that the PMU is supported but the driver is not active. How about 'Enabled'?

I'd also make the strings more unambiguously structured, something like:

	Enabled
	Disabled: Driver error
	Disabled: Driver not loaded
	Disabled: Driver not in kernel config
	Disabled: Not supported by the kernel
	Disabled: Not supported by the hardware
	Disabled: Not supported by the hardware vendor
	Disabled: Not supported by the the architecture
	Disabled: Unknown status

(Note the small changes I did to the text in some places.)

Also note that I'd suggest not enumerating all the error reasons rigidly - just 
have a single error code, but a free flowing error string that is provided by the 
low level driver (and maybe strdup()-ed by the core). That way you can provide 
very specific error descriptions, without having to change the core every time you 
need a new category. Agreed?

Thanks,

	Ingo
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