[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Tue, 7 Jul 2015 10:44:37 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Adrian Hunter <adrian.hunter@...el.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
Andi Kleen <ak@...ux.intel.com>,
Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
Jiri Olsa <jolsa@...hat.com>,
Stephane Eranian <eranian@...gle.com>,
mathieu.poirier@...aro.org, Pawel Moll <pawel.moll@....com>
Subject: Re: [PATCH V3 1/4] perf: Add PERF_RECORD_SWITCH to indicate context
switches
Em Tue, Jul 07, 2015 at 10:25:52AM -0300, Arnaldo Carvalho de Melo escreveu:
> 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?
To help userspace in places where all it has is the union perf_event, we
can reuse one bit in misc to state that, i.e.
#define PERF_RECORD_MISC_SWITCH_NEXT_PREV_PID 14
For instance.
- Arnaldo
> > + * 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,
> > +
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists