linux-kernel - Re: [PATCH] perf/core: move all of the pmu devices into their own location

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Message-ID: <CAP-5=fXwprvLc3ubPmAuyUaTL2aD1frqL+RHJzkp8oe5z85oRw@mail.gmail.com>
Date: Mon, 3 Feb 2025 11:44:13 -0800
From: Ian Rogers <irogers@...gle.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...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>, "Liang, Kan" <kan.liang@...ux.intel.com>
Subject: Re: [PATCH] perf/core: move all of the pmu devices into their own location

On Mon, Feb 3, 2025 at 11:25 AM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> In sysfs, for some reason, all pmu devices seem to show up in the "root"
> of /sys/devices/ making for a confusing mess as these devices are not
> really at the root of the system at all.
>
> Create a fake root devices, "pmu_bus" and place them all under there if
> they do not already have a parent device set, cleaning up sysfs to look
> more sane.
>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Jiri Olsa <jolsa@...nel.org>
> Cc: Ian Rogers <irogers@...gle.com>
> Cc: Adrian Hunter <adrian.hunter@...el.com>
> Cc: "Liang, Kan" <kan.liang@...ux.intel.com>
> Cc: linux-perf-users@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> ---
>
> Note, if you all don't like "pmu_bus" for the name, that's fine, please
> let me know and I can rename it to something else, but it should be
> something to get these objects out of the root sysfs directory.

Excuse my ignorance, does the event_source bus already provide a
similar solution?
```
$ ls /sys/bus/event_source/devices
breakpoint   i915       msr         uncore_arb     uncore_cbox_3
uncore_cbox_7              uprobe
cpu          intel_bts  power       uncore_cbox_0  uncore_cbox_4  uncore_clock
cstate_core  intel_pt   software    uncore_cbox_1  uncore_cbox_5
uncore_imc_free_running_0
cstate_pkg   kprobe     tracepoint  uncore_cbox_2  uncore_cbox_6
uncore_imc_free_running_1
$ ls /sys/devices
breakpoint   intel_pt     platform    uncore_arb     uncore_cbox_5
         uprobe
cpu          isa          pnp0        uncore_cbox_0  uncore_cbox_6
         virtual
cstate_core  kprobe       power       uncore_cbox_1  uncore_cbox_7
cstate_pkg   LNXSYSTM:00  software    uncore_cbox_2  uncore_clock
i915         msr          system      uncore_cbox_3  uncore_imc_free_running_0
intel_bts    pci0000:00   tracepoint  uncore_cbox_4  uncore_imc_free_running_1
```

Thanks,
Ian

>  kernel/events/core.c | 22 +++++++++++++++++++---
>  1 file changed, 19 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index bcb09e011e9e..786537faed2c 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -11767,6 +11767,11 @@ static const struct attribute_group *pmu_dev_groups[] = {
>  };
>
>  static int pmu_bus_running;
> +
> +static struct device pmu_bus_root = {
> +       .init_name      = "pmu_bus",
> +};
> +
>  static struct bus_type pmu_bus = {
>         .name           = "event_source",
>         .dev_groups     = pmu_dev_groups,
> @@ -11790,7 +11795,10 @@ static int pmu_dev_alloc(struct pmu *pmu)
>
>         dev_set_drvdata(pmu->dev, pmu);
>         pmu->dev->bus = &pmu_bus;
> -       pmu->dev->parent = pmu->parent;
> +       if (pmu->parent)
> +               pmu->dev->parent = pmu->parent;
> +       else
> +               pmu->dev->parent = &pmu_bus_root;
>         pmu->dev->release = pmu_dev_release;
>
>         ret = dev_set_name(pmu->dev, "%s", pmu->name);
> @@ -14232,9 +14240,17 @@ static int __init perf_event_sysfs_init(void)
>
>         mutex_lock(&pmus_lock);
>
> -       ret = bus_register(&pmu_bus);
> -       if (ret)
> +       ret = device_register(&pmu_bus_root);
> +       if (ret) {
> +               put_device(&pmu_bus_root);
>                 goto unlock;
> +       }
> +
> +       ret = bus_register(&pmu_bus);
> +       if (ret) {
> +               device_unregister(&pmu_bus_root);
> +               goto unlock;
> +       }
>
>         list_for_each_entry(pmu, &pmus, entry) {
>                 if (pmu->dev)
> --
> 2.48.1
>