Re: [RFC][PATCH 2/2] perf: Add per event clockid support

[Peter Zijlstra <peterz@infradead.org>]

On Fri, Feb 20, 2015 at 03:28:49PM +0000, Pawel Moll wrote:
> On Fri, 2015-02-20 at 14:29 +0000, Peter Zijlstra wrote:
> > @@ -334,8 +335,7 @@ struct perf_event_attr {
> >  	 */
> >  	__u32	sample_stack_user;
> >  
> > -	/* Align to u64. */
> > -	__u32	__reserved_2;
> > +	__u32	clockid;
> 
> I thought about it, but was sort-of-afraid to propose it :-)
> 
> Now, one thing I'm not 100% sure about it is it being unsigned, as
> clockid_t is signed for a reason (negative values have meaning - eg.
> dynamic clocks, which could be useful in some circumstances). Of course
> casting could be an answer, but is there any reason not to make it
> __s32?

I did not spot that significance and cannot find mention of it in
clock_gettime(2) either, but I've no objection to making it __s32.

> > +		default:
> > +			/* XXX add: clock_id_valid() && clock_gettime_ns() ? */
> > +			err = -EINVAL;
> > +			goto err_alloc;
> > +		}
> 
> If you asked me, I'd say -EINVAL, no default.

Yeah, I should probably restructure that a wee bit.