linux-kernel - Re: [PATCH v3 4/7] perf machine: Move machine's threads into its own abstraction

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Message-ID: <CAM9d7cj9CgxmvSMLvDa=RM8zPRJpRbKqMkU7_B68HwEX7qo=hg@mail.gmail.com>
Date: Thu, 29 Feb 2024 17:36:05 -0800
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>, Oliver Upton <oliver.upton@...ux.dev>, 
	Yang Jihong <yangjihong1@...wei.com>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org
Subject: Re: [PATCH v3 4/7] perf machine: Move machine's threads into its own abstraction

On Wed, Feb 28, 2024 at 10:33 PM Ian Rogers <irogers@...gle.com> wrote:
>
> Move thread_rb_node into the machine.c file. This hides the
> implementation of threads from the rest of the code allowing for it to
> be refactored.
>
> Locking discipline is tightened up in this change. As the lock is now
> encapsulated in threads, the findnew function requires holding it (as
> it already did in machine). Rather than do conditionals with locks
> based on whether the thread should be created (which could potentially
> be error prone with a read lock match with a write unlock), have a
> separate threads__find that won't create the thread and only holds the
> read lock. This effectively duplicates the findnew logic, with the
> existing findnew logic only operating under a write lock assuming
> creation is necessary as a previous find failed. The creation may
> still fail with the write lock due to another thread. The duplication
> is removed in a later next patch that delegates the implementation to
> hashtable.
>
> Signed-off-by: Ian Rogers <irogers@...gle.com>

Thanks for doing this!  A nit below..

> ---
[SNIP]
> @@ -3228,27 +3258,31 @@ int thread__resolve_callchain(struct thread *thread,
>         return ret;
>  }
>
> -int machine__for_each_thread(struct machine *machine,
> -                            int (*fn)(struct thread *thread, void *p),
> -                            void *priv)
> +int threads__for_each_thread(struct threads *threads,
> +                            int (*fn)(struct thread *thread, void *data),
> +                            void *data)
>  {
> -       struct threads *threads;
> -       struct rb_node *nd;
> -       int rc = 0;
> -       int i;
> +       for (int i = 0; i < THREADS__TABLE_SIZE; i++) {
> +               struct threads_table_entry *table = &threads->table[i];
> +               struct rb_node *nd;
>
> -       for (i = 0; i < THREADS__TABLE_SIZE; i++) {
> -               threads = &machine->threads[i];
> -               for (nd = rb_first_cached(&threads->entries); nd;
> -                    nd = rb_next(nd)) {
> +               for (nd = rb_first_cached(&table->entries); nd; nd = rb_next(nd)) {
>                         struct thread_rb_node *trb = rb_entry(nd, struct thread_rb_node, rb_node);
> +                       int rc = fn(trb->thread, data);
>
> -                       rc = fn(trb->thread, priv);
>                         if (rc != 0)
>                                 return rc;
>                 }
>         }
> -       return rc;
> +       return 0;

Don't we need locking in this function?

Thanks,
Namhyung


> +
> +}
> +
> +int machine__for_each_thread(struct machine *machine,
> +                            int (*fn)(struct thread *thread, void *p),
> +                            void *priv)
> +{
> +       return threads__for_each_thread(&machine->threads, fn, priv);
>  }
>