Re: [patch] Performance Counters for Linux, v3

[Peter Zijlstra <a.p.zijlstra@chello.nl>]

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.