linux-kernel - Re: [PATCH v3 1/3] perf/core: Rework forwarding of {task|cpu}-clock events

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Date:   Tue, 2 May 2023 17:34:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ravi Bangoria <ravi.bangoria@....com>
Cc:     namhyung@...nel.org, eranian@...gle.com, acme@...nel.org,
        mark.rutland@....com, jolsa@...nel.org, irogers@...gle.com,
        bp@...en8.de, kan.liang@...ux.intel.com, adrian.hunter@...el.com,
        maddy@...ux.ibm.com, x86@...nel.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        sandipan.das@....com, ananth.narayan@....com,
        santosh.shukla@....com
Subject: Re: [PATCH v3 1/3] perf/core: Rework forwarding of {task|cpu}-clock
 events

On Tue, Apr 25, 2023 at 07:52:03PM +0530, Ravi Bangoria wrote:
> Currently, PERF_TYPE_SOFTWARE is treated specially since task-clock and
> cpu-clock events are interfaced through it but internally gets forwarded
> to their own pmus.
> 
> Rework this by overwriting event->attr.type in perf_swevent_init() which
> will cause perf_init_event() to retry with updated type and event will
> automatically get forwarded to right pmu. With the change, SW pmu no
> longer needs to be treated specially and can be included in 'pmu_idr'
> list.
> 
> Suggested-by: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@....com>
> ---
>  include/linux/perf_event.h | 11 ++++++
>  kernel/events/core.c       | 69 ++++++++++++++++++++------------------
>  2 files changed, 47 insertions(+), 33 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index d5628a7b5eaa..40647d707fb3 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -322,6 +322,9 @@ struct pmu {
>  	/* number of address filters this PMU can do */
>  	unsigned int			nr_addr_filters;
>  
> +	/* Skip creating pmu device and sysfs interface. */
> +	bool				skip_sysfs_dev;
> +
>  	/*
>  	 * Fully disable/enable this PMU, can be used to protect from the PMI
>  	 * as well as for lazy/batch writing of the MSRs.

Does this make sense?

---
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -295,6 +295,8 @@ struct perf_event_pmu_context;
 
 struct perf_output_handle;
 
+#define PMU_NULL_DEV	((void *)(~0))
+
 /**
  * struct pmu - generic performance monitoring unit
  */
@@ -322,9 +324,6 @@ struct pmu {
 	/* number of address filters this PMU can do */
 	unsigned int			nr_addr_filters;
 
-	/* Skip creating pmu device and sysfs interface. */
-	bool				skip_sysfs_dev;
-
 	/*
 	 * Fully disable/enable this PMU, can be used to protect from the PMI
 	 * as well as for lazy/batch writing of the MSRs.
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11113,7 +11113,7 @@ static struct pmu perf_cpu_clock = {
 	.task_ctx_nr	= perf_sw_context,
 
 	.capabilities	= PERF_PMU_CAP_NO_NMI,
-	.skip_sysfs_dev	= true,
+	.dev		= PMU_NULL_DEV,
 
 	.event_init	= cpu_clock_event_init,
 	.add		= cpu_clock_event_add,
@@ -11195,7 +11195,7 @@ static struct pmu perf_task_clock = {
 	.task_ctx_nr	= perf_sw_context,
 
 	.capabilities	= PERF_PMU_CAP_NO_NMI,
-	.skip_sysfs_dev	= true,
+	.dev		= PMU_NULL_DEV,
 
 	.event_init	= task_clock_event_init,
 	.add		= task_clock_event_add,
@@ -11442,7 +11442,7 @@ int perf_pmu_register(struct pmu *pmu, c
 	type = ret;
 	pmu->type = type;
 
-	if (pmu_bus_running && !pmu->skip_sysfs_dev) {
+	if (pmu_bus_running && !pmu->dev) {
 		ret = pmu_dev_alloc(pmu);
 		if (ret)
 			goto free_idr;
@@ -11524,7 +11524,7 @@ void perf_pmu_unregister(struct pmu *pmu
 
 	free_percpu(pmu->pmu_disable_count);
 	idr_remove(&pmu_idr, pmu->type);
-	if (pmu_bus_running) {
+	if (pmu_bus_running && pmu->dev != PMU_NULL_DEV) {
 		if (pmu->nr_addr_filters)
 			device_remove_file(pmu->dev, &dev_attr_nr_addr_filters);
 		device_del(pmu->dev);
@@ -13687,7 +13687,7 @@ static int __init perf_event_sysfs_init(
 		goto unlock;
 
 	list_for_each_entry(pmu, &pmus, entry) {
-		if (pmu->skip_sysfs_dev)
+		if (pmu->dev)
 			continue;
 
 		ret = pmu_dev_alloc(pmu);