On Fri, 2015-02-20 at 14:29 +0000, Peter Zijlstra wrote:
> The below patch makes the distinction between these two cases by
> adding perf_event_clock() which is used for the second case. It
> further makes this configurable on a per-event basis, but adds a few
> sanity checks such that we cannot combine events with different clocks
> in confusing ways.
The idea works for me (obviously :-)
> And since we then have per-event configurability we might as well
> retain the 'legacy' behaviour as a default.
Don't mind that at all.
> @@ -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?
> + default:
> + /* XXX add: clock_id_valid() && clock_gettime_ns() ? */
> + err = -EINVAL;
> + goto err_alloc;
> + }
If you asked me, I'd say -EINVAL, no default.
Cheers!
Pawel
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