Em Tue, Jul 07, 2015 at 11:36:39AM +0300, Adrian Hunter escreveu:
> To make the event useful for privileged users also, if the
> context is cpu-wide then the event will also provide the
> next or previous pid/tid.
<SNIP>
> + /*
> + * Records a context switch in or out (flagged by
> + * PERF_RECORD_MISC_SWITCH_OUT). next_prev_pid and next_prev_tid are
> + * (u32)-1 unless the context is cpu-wide, in which case they are the
Why carry those extra 8 bytes for non priviledged users, all the time
with -1?
Can't userspace cope with this, i.e. we should be able to look for those
fields when the context is CPU wide, and to not look for them otherwise,
no?
> + * next (switching out) or previous (switching in) pid/tid.
> + *
> + * struct {
> + * struct perf_event_header header;
> + * u32 next_prev_pid;
> + * u32 next_prev_tid;
> + * struct sample_id sample_id;
> + * };
> + */
> + PERF_RECORD_SWITCH = 14,
> +
- Arnaldo
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