linux-kernel - Re: [PATCH v3 1/4] perf: add active_entry list head to struct perf

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Date:	Sat, 26 Oct 2013 18:57:37 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	"Yan, Zheng" <zheng.z.yan@...el.com>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v3 1/4] perf: add active_entry list head to struct perf_event

On Fri, Oct 25, 2013 at 4:56 PM, Jiri Olsa <jolsa@...hat.com> wrote:
>
> On Wed, Oct 23, 2013 at 02:58:02PM +0200, Stephane Eranian wrote:
> > This patch adds a new fields to the struct perf_event.
> > It is intended to be used to chain events which are
> > active (enabled). It helps in the hardware layer
> > for PMU which do not have actual counter restrictions, i.e.,
> > free running read-only counters. Active events are chained
> > as opposed to being tracked via the counter they use.
> >
> > Signed-off-by: Stephane Eranian <eranian@...gle.com>
> > ---
> >  include/linux/perf_event.h |    1 +
> >  kernel/events/core.c       |    1 +
> >  2 files changed, 2 insertions(+)
> >
> > diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> > index 2e069d1..a376384 100644
> > --- a/include/linux/perf_event.h
> > +++ b/include/linux/perf_event.h
> > @@ -435,6 +435,7 @@ struct perf_event {
> >       struct perf_cgroup              *cgrp; /* cgroup event is attach to */
> >       int                             cgrp_defer_enabled;
> >  #endif
> > +     struct list_head                active_entry;
>
> Could this be in union with 'hlist_entry' ? It looks
> as 'same purpose' and 'mutualy exclusive stuff.
>
You're saying that I could use the hlist_entry field because
it is currently only used by the sw events in the generic layer.
But it seems to be a complicated rcu list for the purpose here.
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