linux-kernel - Re: [PATCH] x86, perf, nmi: Disable perf if counters are not accessable

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Message-ID: <20101123141305.GA17346@redhat.com>
Date:	Tue, 23 Nov 2010 09:13:05 -0500
From:	Don Zickus <dzickus@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, jason.wessel@...driver.com,
	gorcunov@...il.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, perf, nmi:  Disable perf if counters are not
 accessable

On Tue, Nov 23, 2010 at 11:46:06AM +0100, Peter Zijlstra wrote:
> On Mon, 2010-11-22 at 16:55 -0500, Don Zickus wrote:
> > +static bool check_hw_exists(void)
> > +{
> > +       u64 val, val_new;
> > +
> > +       val = 0xabcdUL;
> > +       (void) checking_wrmsrl(x86_pmu.perfctr, val);
> > +       rdmsrl_safe(x86_pmu.perfctr, &val_new);
> > +       if (val != val_new)
> > +               return false;
> > +
> > +       return true;
> > +} 
> 
> If I can make any sense of the implementation of native_read_msr_safe()
> then I think it doesn't actually sets val_new in case it faults, it just
> returns -EIO.
> 
> So I changed it to:
> 
> static bool check_hw_exists(void)
> {
>         u64 val, val_new = 0;
>         int ret = 0;
> 
>         val = 0xabcdUL;
>         ret |= checking_wrmsrl(x86_pmu.perfctr, val);
>         ret |= rdmsrl_safe(x86_pmu.perfctr, &val_new);
>         if (ret || val != val_new)
>                 return false;
> 
>         return true;
> }
> 
> And have applied the patch,

Looks good to me.  Thanks!

Cheers,
Don
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