Subject: Re: [patch] Performance Counters for Linux, v3
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Ingo Molnar <mingo@elte.hu>
Cc: Tony Luck <tony.luck@intel.com>, linux-kernel@vger.kernel.org,
       Thomas Gleixner <tglx@linutronix.de>,
       Andrew Morton <akpm@linux-foundation.org>,
       Stephane Eranian <eranian@googlemail.com>,
       Eric Dumazet <dada1@cosmosbay.com>,
       Robert Richter <robert.richter@amd.com>,
       Arjan van de Veen <arjan@infradead.org>, Peter Anvin <hpa@zytor.com>,
       Paul Mackerras <paulus@samba.org>,
       "David S. Miller" <davem@davemloft.net>
In-Reply-To: <20081211193439.GA25986@elte.hu>
References: <20081211155230.GA4230@elte.hu>
	 <12c511ca0812111111t2992dd2cw8b4d57ac57bd0700@mail.gmail.com>
	 <20081211193439.GA25986@elte.hu>
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Date: Fri, 12 Dec 2008 09:29:30 +0100
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On Thu, 2008-12-11 at 20:34 +0100, Ingo Molnar wrote:

>  struct perf_counter_hw_event {
>         s64                     type;
> 
>         u64                     irq_period;
>         u32                     record_type;
> 
>         u32                     disabled     :  1, /* off by default */
>                                 nmi          :  1, /* NMI sampling   */
>                                 raw          :  1, /* raw event type */
>                                 __reserved_1 : 29;
> 
>         u64                     __reserved_2;
>  };
> 
> if the hw_event.raw bit is set to 1, then the hw_event.type is fully 
> 'raw'. The default is for raw to be 0. So negative numbers can be used 
> for sw events, positive numbers for hw events. Both can be extended 
> gradually, without arbitrarily limits introduced.

On that, I still don't think its a good idea to use bitfields in an ABI.
The C std is just not strict enough on them, and I guess that is the
reason this would be the first such usage.

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