linux-kernel - Re: [tip:perf/core] perf/x86: Add an MSR PMU driver

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Date:	Thu, 6 Aug 2015 08:30:08 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	"Liang, Kan" <kan.liang@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Lutomirski <luto@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:perf/core] perf/x86: Add an MSR PMU driver

On Thu, Aug 6, 2015 at 8:21 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, Aug 04, 2015 at 08:39:27PM +0000, Liang, Kan wrote:
> -       default:
> -               err = -ENOTSUPP;
> +               if (!msr[i].test() || rdmsrl_safe(msr[i].msr, &val))
> +                       msr[i].attr = NULL;

IIRC rdmsrl_safe literally never fails under QEMU TCG, and I'm not
entirely sure what happens under KVM if emulation kicks in.  It might
pay to keep the model check for the non-architectural stuff, or at
least check for a nonzero return value.

--Andy
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