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From: Ben Gainey <ben.gainey@arm.com>
To: linux-perf-users@vger.kernel.org,
	linux-kernel@vger.kernel.org
Cc: peterz@infradead.org,
	mingo@redhat.com,
	acme@kernel.org,
	mark.rutland@arm.com,
	alexander.shishkin@linux.intel.com,
	jolsa@kernel.org,
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	irogers@google.com,
	adrian.hunter@intel.com,
	james.clark@arm.com,
	Ben Gainey <ben.gainey@arm.com>
Subject: [PATCH 1/1] perf: Support PERF_SAMPLE_READ with inherit_stat
Date: Fri, 19 Jan 2024 16:39:24 +0000
Message-ID: <20240119163924.2801678-2-ben.gainey@arm.com>
In-Reply-To: <20240119163924.2801678-1-ben.gainey@arm.com>
References: <20240119163924.2801678-1-ben.gainey@arm.com>
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This change allows events to use PERF_SAMPLE READ with inherit
so long as both inherit_stat and PERF_SAMPLE_TID are set.

In this configuration, and event will be inherited into any
child processes / threads, allowing convenient profiling of a
multi-process or multi-threaded application, whilst allowing
profiling tools to collect per-thread samples, in particular
of groups of counters.

Signed-off-by: Ben Gainey <ben.gainey@arm.com>
---
 kernel/events/core.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9efd0d7775e7c..4b603463d888f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -11988,10 +11988,13 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
 	local64_set(&hwc->period_left, hwc->sample_period);
 
 	/*
-	 * We currently do not support PERF_SAMPLE_READ on inherited events.
+	 * We do not support PERF_SAMPLE_READ on inherited events unless
+	 * inherit_stat and PERF_SAMPLE_TID are also selected, which allows
+	 * inherited events to collect per-thread samples.
 	 * See perf_output_read().
 	 */
-	if (attr->inherit && (attr->sample_type & PERF_SAMPLE_READ))
+	if (attr->inherit && (attr->sample_type & PERF_SAMPLE_READ)
+		&& !(attr->inherit_stat && (attr->sample_type & PERF_SAMPLE_TID)))
 		goto err_ns;
 
 	if (!has_branch_stack(event))
-- 
2.43.0