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

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Message-ID: <20131026174426.GD1069@krava.brq.redhat.com>
Date:	Sat, 26 Oct 2013 19:44:26 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Stephane Eranian <eranian@...gle.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 Sat, Oct 26, 2013 at 06:57:37PM +0200, Stephane Eranian wrote:
> 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.

nope, I just meant saving little space like:

union {
	struct list_head                active_entry;
        struct hlist_node               hlist_entry;
}

just a nitpick

jirka
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