linux-kernel - [PATCH v11 2/5] perf: Add a counter for number of user access events in context

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Date:   Tue, 19 Oct 2021 18:19:04 -0500
From:   Rob Herring <robh@...nel.org>
To:     Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Vince Weaver <vincent.weaver@...ne.edu>,
        honnappa.nagarahalli@....com, Zachary.Leaf@....com,
        Catalin Marinas <catalin.marinas@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-perf-users@...r.kernel.org
Subject: [PATCH v11 2/5] perf: Add a counter for number of user access events in context

For controlling user space counter access, we need to know if any event
in a context (currently scheduled or not) is using user space counters.
Walking the context's list of events would be slow, so add a counter
to track this.

Reviewed-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Rob Herring <robh@...nel.org>
---
v10:
 - Re-added.
 - Maintain the count in the perf core
v9:
 - Dropped
v8:
 - new patch
---
 include/linux/perf_event.h | 1 +
 kernel/events/core.c       | 4 ++++
 2 files changed, 5 insertions(+)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 34ebcc9af608..d733cac749e2 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -828,6 +828,7 @@ struct perf_event_context {
 
 	int				nr_events;
 	int				nr_active;
+	int				nr_user;
 	int				is_active;
 	int				nr_stat;
 	int				nr_freq;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 744e8726c5b2..01290d150da3 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -1808,6 +1808,8 @@ list_add_event(struct perf_event *event, struct perf_event_context *ctx)
 
 	list_add_rcu(&event->event_entry, &ctx->event_list);
 	ctx->nr_events++;
+	if (event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT)
+		ctx->nr_user++;
 	if (event->attr.inherit_stat)
 		ctx->nr_stat++;
 
@@ -1999,6 +2001,8 @@ list_del_event(struct perf_event *event, struct perf_event_context *ctx)
 	event->attach_state &= ~PERF_ATTACH_CONTEXT;
 
 	ctx->nr_events--;
+	if (event->hw.flags & PERF_EVENT_FLAG_USER_READ_CNT)
+		ctx->nr_user--;
 	if (event->attr.inherit_stat)
 		ctx->nr_stat--;
 
-- 
2.32.0