linux-kernel - Re: [PATCH v3 04/10] perf: Add per perf_cpu_context min

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Date:   Fri, 15 Nov 2019 17:19:48 -0800
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 04/10] perf: Add per perf_cpu_context min_heap storage

On Thu, Nov 14, 2019 at 1:51 AM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Nov 13, 2019 at 04:30:36PM -0800, Ian Rogers wrote:
> > +     if (cpuctx) {
> > +             event_heap = (struct min_max_heap){
> > +                     .data = cpuctx->itr_storage,
> > +                     .size = 0,
>
> C guarantees that unnamed fields get to be 0

Agreed, this is kept here to aid readability. Do you feel strongly
about not having this? It appears to be kept elsewhere for clarity
too:
$ grep -r "\..*= 0," arch/ kernel/ tools/|wc -l
2528

> > +                     .cap = cpuctx->itr_storage_cap,
> > +             };
> > +     } else {
> > +             event_heap = (struct min_max_heap){
> > +                     .data = itrs,
> > +                     .size = 0,
>
> idem.
>
> > +                     .cap = ARRAY_SIZE(itrs),
> > +             };
> > +             /* Events not within a CPU context may be on any CPU. */
> > +             __heap_add(&event_heap, perf_event_groups_first(groups, -1));
> > +
>
> suprious whitespace

Done.



> > +     }
> > +     evt = event_heap.data;
> > +
> >       __heap_add(&event_heap, perf_event_groups_first(groups, cpu));