linux-kernel - Re: [PATCH v6 1/6] perf/cgroup: Reorder perf_cgroup

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Message-ID: <20200214173734.GN14914@hirez.programming.kicks-ass.net>
Date:   Fri, 14 Feb 2020 18:37:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Shuah Khan <skhan@...uxfoundation.org>
Cc:     Ian Rogers <irogers@...gle.com>, 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>,
        Randy Dunlap <rdunlap@...radead.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Marco Elver <elver@...gle.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Gary Hook <Gary.Hook@....com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v6 1/6] perf/cgroup: Reorder perf_cgroup_connect()

On Fri, Feb 14, 2020 at 09:11:24AM -0700, Shuah Khan wrote:
> On 2/14/20 12:51 AM, Ian Rogers wrote:
> > From: Peter Zijlstra <peterz@...radead.org>
> > 
> > Move perf_cgroup_connect() after perf_event_alloc(), such that we can
> > find/use the PMU's cpu context.
> 
> Can you elaborate on this usage? It will helpful to know how
> this is used and what do we get from it. What were we missing
> with the way it was done before?

It says so right there. We need it after perf_event_alloc() so that we
can find/use the event's PMU cpu context.