linux-kernel - Re: [PATCH v2 1/2] perf symbol: Remove symbol_name_rb

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Date:   Wed, 21 Jun 2023 20:51:00 -0700
From:   Namhyung Kim <namhyung@...nel.org>
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@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Yang Jihong <yangjihong1@...wei.com>,
        Carsten Haitzler <carsten.haitzler@....com>,
        Changbin Du <changbin.du@...wei.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Jason Wang <wangborong@...rlc.com>,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] perf symbol: Remove symbol_name_rb_node

Hi Ian,

On Tue, Jun 20, 2023 at 11:37 PM Ian Rogers <irogers@...gle.com> wrote:
>
> Most perf commands want to sort symbols by name and this is done via
> an invasive rbtree that on 64-bit systems costs 24 bytes. Sorting the
> symbols in a DSO by name is optional and not done by default, however,
> if sorting is requested the 24 bytes is allocated for every
> symbol.
>
> This change removes the rbtree and uses a sorted array of symbol
> pointers instead (costing 8 bytes per symbol). As the array is created
> on demand then there are further memory savings. The complexity of
> sorting the array and using the rbtree are the same.
>
> To support going to the next symbol, the index of the current symbol
> needs to be passed around as a pair with the current symbol. This
> requires some API changes.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>
>
> v2. map__find_symbol_by_name_idx so that map__find_symbol_by_name
>     doesn't need an optional parameter. Separate out
>     symbol_conf.sort_by_name removal.
> ---

[SNIP]
>  void dso__sort_by_name(struct dso *dso)
>  {
> -       dso__set_sorted_by_name(dso);
> -       return symbols__sort_by_name(&dso->symbol_names, &dso->symbols);
> +       mutex_lock(&dso->lock);
> +       if (!dso__sorted_by_name(dso)) {
> +               size_t len;
> +
> +               dso->symbol_names = symbols__sort_by_name(&dso->symbols, &len);
> +               if (dso->symbol_names) {
> +                       dso->symbol_names_len = len;
> +                       dso__set_sorted_by_name(dso);
> +               }
> +       }
> +       mutex_unlock(&dso->lock);

I think this part deserves a separate commit.

Thanks,
Namhyung