linux-kernel - Re: [PATCH v3 08/10] perf: cache perf_event_groups

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Date:   Mon, 18 Nov 2019 09:37:33 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Kees Cook <keescook@...omium.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Petr Mladek <pmladek@...e.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Qian Cai <cai@....pw>, Joe Lawrence <joe.lawrence@...hat.com>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        "Uladzislau Rezki (Sony)" <urezki@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Gary Hook <Gary.Hook@....com>, Arnd Bergmann <arnd@...db.de>,
        Kan Liang <kan.liang@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v3 08/10] perf: cache perf_event_groups_first for cgroups

On Fri, Nov 15, 2019 at 05:20:52PM -0800, Ian Rogers wrote:
> On Thu, Nov 14, 2019 at 2:25 AM Peter Zijlstra <peterz@...radead.org> wrote:

> > > @@ -1706,18 +1738,10 @@ perf_event_groups_first(struct perf_event_groups *groups, int cpu,
> > >                       continue;
> > >               }
> > >  #ifdef CONFIG_CGROUP_PERF
> > > -             node_cgrp_id = 0;
> > > -             if (node_event->cgrp && node_event->cgrp->css.cgroup)
> > > -                     node_cgrp_id = node_event->cgrp->css.cgroup->id;
> > > -
> > > -             if (cgrp_id < node_cgrp_id) {
> > > +             if (node_event->cgrp) {
> > >                       node = node->rb_left;
> > >                       continue;
> > >               }
> > > -             if (cgrp_id > node_cgrp_id) {
> > > -                     node = node->rb_right;
> > > -                     continue;
> > > -             }
> > >  #endif
> > >               match = node_event;
> > >               node = node->rb_left;
> >
> > Also, just leave that in and let callers have: .cgrp = NULL. Then you
> > can forgo that monstrous name.
> 
> Done. It is a shame that there is some extra logic for the task/no-cgroup case.

Yes, OTOH the primitive is consistent and more generic and possibly the
compiler will notice and fix it for us, it is a static function after
all, so it can be more agressive.