linux-kernel - [RFC PATCH v2 0/2] perf tools: Don't set inherit bit for system wide evsel

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Date:	Mon, 26 Oct 2015 11:41:58 +0000
From:	Wang Nan <wangnan0@...wei.com>
To:	<acme@...nel.org>, <ast@...mgrid.com>, <adrian.hunter@...el.com>
CC:	<linux-kernel@...r.kernel.org>, <pi3orama@....com>,
	<lizefan@...wei.com>, Wang Nan <wangnan0@...wei.com>
Subject: [RFC PATCH v2 0/2] perf tools: Don't set inherit bit for system wide evsel

Previous version can be found from [1].

To make bpf_perf_event_output() and bpf_perf_event_read() easier to be
used, these two patches set inherit to 0 for system wide evsels.
After applying them, users are possible to pass system wide events to
BPF programs in following command, and don't need to consider the
setting of inherit:

 # perf record -a -e evt=cycles -e ./test__map.c/maps.pmu_map.event=evt/ ...

Patch 1/2 set evsel->system_wide for system wide target. I have checked
in current evlist.c and evsel.c. The only behavior change I found is in
evlist.c:

		/*
		 * The system_wide flag causes a selected event to be opened
		 * always without a pid.  Consequently it will never get a
		 * POLLHUP, but it is used for tracking in combination with
		 * other events, so it should not need to be polled anyway.
		 * Therefore don't add it for polling.
		 */
		if (!evsel->system_wide &&
		    __perf_evlist__add_pollfd(evlist, fd, idx) < 0) {
			perf_evlist__mmap_put(evlist, idx);
			return -1;
		}

With patch 1/2, __perf_evlist__add_pollfd() won't be called. From the
comment I pasted this modification looks harmless.

[1] http://lkml.kernel.org/r/1445597029-133332-1-git-send-email-wangnan0@huawei.com

Wang Nan (2):
  perf tools: Set evsel->system_wide field for global system wide
    recording
  perf tools: Don't set inherit bit for system wide evsel

 tools/perf/util/evsel.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

-- 
1.8.3.4

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