linux-kernel - Re: [PATCH v6 3/6] perf: Use min_heap in visit_groups

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Date:   Mon, 17 Feb 2020 18:23:11 +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>,
        Randy Dunlap <rdunlap@...radead.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        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 3/6] perf: Use min_heap in visit_groups_merge

On Thu, Feb 13, 2020 at 11:51:30PM -0800, Ian Rogers wrote:
>  
> -		*evt = perf_event_groups_next(*evt);
> +		next = perf_event_groups_next(itrs[0]);
> +		if (next) {
> +			min_heap_pop_push(&event_heap, &next,
> +					&perf_min_heap);
> +		} else
> +			min_heap_pop(&event_heap, &perf_min_heap);
>  	}

Like this:

@@ -3585,9 +3581,9 @@ static noinline int visit_groups_merge(s
 		if (ret)
 			return ret;
 
-		next = perf_event_groups_next(*evt);
-		if (next)
-			min_heap_pop_push(&event_heap, &next, &perf_min_heap);
+		*evt = perf_event_groups_next(*evt);
+		if (*evt)
+			min_heapify(&event_heap, 0, &perf_min_heap);
 		else
 			min_heap_pop(&event_heap, &perf_min_heap);
 	}

That's an 'obvious' replace and resort and obviates the need for that
weird pop that doesn't return nothing operation.