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

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Message-ID: <CALCETrXffVT=KQpURGLEAXH5x6KxXhYuicGgk3hmF8-QGT81jw@mail.gmail.com>
Date:	Tue, 4 Aug 2015 07:50:21 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	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>,
	Peter Zijlstra <peterz@...radead.org>,
	"Liang, Kan" <kan.liang@...el.com>, Ingo Molnar <mingo@...nel.org>
Cc:	"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 Tue, Aug 4, 2015 at 2:01 AM, tip-bot for Andy Lutomirski
<tipbot@...or.com> wrote:
> Commit-ID:  b7b7c7821d932ba18ef6c8eafc8536066b4c2ef4
> Gitweb:     http://git.kernel.org/tip/b7b7c7821d932ba18ef6c8eafc8536066b4c2ef4
> Author:     Andy Lutomirski <luto@...nel.org>

I think I'm slightly late to the party reviewing what appears to be my
own code :)

> --- /dev/null
> +++ b/arch/x86/kernel/cpu/perf_event_msr.c
> @@ -0,0 +1,242 @@
> +#include <linux/perf_event.h>
> +
> +enum perf_msr_id {
> +       PERF_MSR_TSC                    = 0,
> +       PERF_MSR_APERF                  = 1,
> +       PERF_MSR_MPERF                  = 2,
> +       PERF_MSR_PPERF                  = 3,
> +       PERF_MSR_SMI                    = 4,
> +
> +       PERF_MSR_EVENT_MAX,
> +};
> +
> +struct perf_msr {
> +       int     id;
> +       u64     msr;
> +};
> +
> +static struct perf_msr msr[] = {
> +       { PERF_MSR_TSC, 0 },
> +       { PERF_MSR_APERF, MSR_IA32_APERF },
> +       { PERF_MSR_MPERF, MSR_IA32_MPERF },
> +       { PERF_MSR_PPERF, MSR_PPERF },
> +       { PERF_MSR_SMI, MSR_SMI_COUNT },
> +};

I think this could be easier to work with if it were [PERF_MSR_TSC] =
{...}, etc.  No big deal, though, until the list gets long.  However,
it might make fixing the apparent issue below easier...

> +static int msr_event_init(struct perf_event *event)
> +{
> +       u64 cfg = event->attr.config;

...

> +       event->hw.event_base = msr[cfg].msr;

Shouldn't this verify that the fancy enumeration code actually
believes that msr[cfg] exists on this system?  Otherwise we might have
a very short wait until the perf fuzzer oopses this thing :)

--Andy
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