linux-kernel - Re: [PATCH v2 7/7] perf expr: Migrate expr ids table to a hashmap

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Date:   Fri, 15 May 2020 12:39:34 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        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>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Kajol Jain <kjain@...ux.ibm.com>,
        Andi Kleen <ak@...ux.intel.com>,
        John Garry <john.garry@...wei.com>,
        Jin Yao <yao.jin@...ux.intel.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Kim Phillips <kim.phillips@....com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Leo Yan <leo.yan@...aro.org>,
        open list <linux-kernel@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 7/7] perf expr: Migrate expr ids table to a hashmap

On Fri, May 15, 2020 at 9:51 AM Ian Rogers <irogers@...gle.com> wrote:
>
> Use a hashmap between a char* string and a double* value. While bpf's
> hashmap entries are size_t in size, we can't guarantee sizeof(size_t) >=
> sizeof(double). Avoid a memory allocation when gathering ids by making 0.0
> a special value encoded as NULL.
>
> Original map suggestion by Andi Kleen:
> https://lore.kernel.org/lkml/20200224210308.GQ160988@tassilo.jf.intel.com/
> and seconded by Jiri Olsa:
> https://lore.kernel.org/lkml/20200423112915.GH1136647@krava/
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
> ---
>  tools/perf/tests/expr.c       |  40 ++++++-----
>  tools/perf/tests/pmu-events.c |  25 +++----
>  tools/perf/util/expr.c        | 129 +++++++++++++++++++---------------
>  tools/perf/util/expr.h        |  26 +++----
>  tools/perf/util/expr.y        |  22 +-----
>  tools/perf/util/metricgroup.c |  87 +++++++++++------------
>  tools/perf/util/stat-shadow.c |  49 ++++++++-----
>  7 files changed, 197 insertions(+), 181 deletions(-)
>
> diff --git a/tools/perf/tests/expr.c b/tools/perf/tests/expr.c
> index 3f742612776a..5e606fd5a2c6 100644
> --- a/tools/perf/tests/expr.c
> +++ b/tools/perf/tests/expr.c
> @@ -19,11 +19,9 @@ static int test(struct expr_parse_ctx *ctx, const char *e, double val2)
>  int test__expr(struct test *t __maybe_unused, int subtest __maybe_unused)
>  {
>         const char *p;
> -       const char **other;
> -       double val;
> -       int i, ret;
> +       double val, *val_ptr;
> +       int ret;
>         struct expr_parse_ctx ctx;
> -       int num_other;
>
>         expr__ctx_init(&ctx);
>         expr__add_id(&ctx, "FOO", 1);
> @@ -52,25 +50,29 @@ int test__expr(struct test *t __maybe_unused, int subtest __maybe_unused)
>         ret = expr__parse(&val, &ctx, p, 1);
>         TEST_ASSERT_VAL("missing operand", ret == -1);
>
> +       hashmap__clear(&ctx.ids);

hashmap__clear() will free up memory allocated for hashmap itself and
hash entries, but not keys/values. Unless it's happening somewhere
else, you'll need to do something similar to expr__ctx_clear() below?

Same below for another "lone" hashmap_clear() call.

>         TEST_ASSERT_VAL("find other",
> -                       expr__find_other("FOO + BAR + BAZ + BOZO", "FOO", &other, &num_other, 1) == 0);

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