linux-kernel - [PATCH v3 2/3] perf: Document PERF_EVENT_IOC_INC_EVENT

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Message-Id: <20250106-perf_set_event_limit-v3-2-dbde0e90ddde@rivosinc.com>
Date: Mon, 06 Jan 2025 20:07:33 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: 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>, Ian Rogers <irogers@...gle.com>, 
 Adrian Hunter <adrian.hunter@...el.com>, Atish Patra <atishp@...osinc.com>
Cc: linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Charlie Jenkins <charlie@...osinc.com>
Subject: [PATCH v3 2/3] perf: Document PERF_EVENT_IOC_INC_EVENT_LIMIT

Introduce PERF_EVENT_IOC_INC_EVENT_LIMIT and explain the differences
between it and PERF_EVENT_IOC_REFRESH.

Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
---
 tools/perf/design.txt | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/tools/perf/design.txt b/tools/perf/design.txt
index aa8cfeabb7432d4011005f34a981fa3381caab09..1626ae83785a5773c255cc5219c2e9e0525dda19 100644
--- a/tools/perf/design.txt
+++ b/tools/perf/design.txt
@@ -439,6 +439,11 @@ Additionally, non-inherited overflow counters can use
 
 to enable a counter for 'nr' events, after which it gets disabled again.
 
+PERF_EVENT_IOC_REFRESH will increment the event limit by 'nr' and enable the
+event. To increment the event limit without enabling it, use the following:
+
+	ioctl(fd, PERF_EVENT_IOC_INC_EVENT_LIMIT, nr);
+
 A process can enable or disable all the counter groups that are
 attached to it, using prctl:
 

-- 
2.34.1