linux-kernel - Re: [PATCH 1/3] perf: disable sampled events if no PMU interrupt

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Date:	Tue, 20 May 2014 11:12:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Will Deacon <will.deacon@....com>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH 1/3] perf: disable sampled events if no PMU interrupt

On Fri, May 16, 2014 at 05:12:12PM -0400, Vince Weaver wrote:
> 
> Add common code to generate ENOTSUPP at event creation time if an 
> architecture attempts to create a sampled event and PERF_PMU_NO_INTERRUPT
> is set.
> 
> This adds a new pmu->capabilities flag.  
> Initially we only support PERF_PMU_NO_INTERRUPT (to indicate a PMU
> has no support for generating hardware interrupts) but there are 
> other capabilities that can be added later.
> 
> Signed-off-by: Vince Weaver <vincent.weaver@...ne.edu>
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 3356abc..2164763 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -251,9 +251,20 @@ struct pmu {
>  	 * flush branch stack on context-switches (needed in cpu-wide mode)
>  	 */
>  	void (*flush_branch_stack)	(void);
> +
> +	/*
> +	 * various common per-pmu feature flags
> +	 */
> +	int capabilities;

As suggested by Will, I've put it in a 4 byte hole earlier in the
structure.

>  };
>  
>  /**
> + * struct pmu->capabilites flags

Due to braindamage from years of C++ coding, many other comments refer
to members using the C++ :: notation, so I've changed that to be
consistent and read: pmu::capabilities.

> + */
> +#define PERF_PMU_NO_INTERRUPT		1

Are you ok with me making that:

#define PERF_PMU_CAP_NO_INTERRUPT		0x01


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