linux-kernel - Re: [patch] Performance Counters for Linux, v3

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Date:	Fri, 12 Dec 2008 09:29:30 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Stephane Eranian <eranian@...glemail.com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Robert Richter <robert.richter@....com>,
	Arjan van de Veen <arjan@...radead.org>,
	Peter Anvin <hpa@...or.com>, Paul Mackerras <paulus@...ba.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [patch] Performance Counters for Linux, v3

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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