perf record: Add a function to test for kernel support for AUX area sampling (9bca1a4e) · Commits · 戴 / test

Architectures are expected to know if AUX area sampling is supported by the hardware. Add a function perf_can_aux_sample() which will determine whether the kernel supports it. Committer notes: I reported that this message was taking place on a kernel without the required bits: # perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' Error: The sys_perf_event_open() syscall returned with 7 (Argument list too long) for event (branch-misses:u). /bin/dmesg | grep -i perf may provide additional information. Adrian sent a patch addressing it, with this explanation: ---- perf_can_aux_sample_size() always returned true because it did not pass the attribute size to sys_perf_event_open, nor correctly check the return value and errno. ---- After applying it I get, later in the series, when --aux-sample is added: # perf record --aux-sample -e '{intel_pt//u,branch-misses:u}' AUX area sampling is not supported by kernel Signed-off-by:

Adrian Hunter <adrian.hunter@intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Link: http://lore.kernel.org/lkml/20191115124225.5247-4-adrian.hunter@intel.com Signed-off-by:

Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evlist.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -176,6 +176,7 @@ void perf_evlist__set_id_pos(struct evlist *evlist);
		bool perf_can_sample_identifier(void);
		bool perf_can_record_switch_events(void);
		bool perf_can_record_cpu_wide(void);
		bool perf_can_aux_sample(void);
		void perf_evlist__config(struct evlist evlist, struct record_opts opts,
		struct callchain_param *callchain);
		int record_opts__config(struct record_opts *opts);

tools/perf/util/record.c

+31 −0

Original line number	Diff line number	Diff line
		@@ -136,6 +136,37 @@ bool perf_can_record_cpu_wide(void)
		return true;
		}

		/*
		* Architectures are expected to know if AUX area sampling is supported by the
		* hardware. Here we check for kernel support.
		*/
		bool perf_can_aux_sample(void)
		{
		struct perf_event_attr attr = {
		.size = sizeof(struct perf_event_attr),
		.exclude_kernel = 1,
		/*
		* Non-zero value causes the kernel to calculate the effective
		* attribute size up to that byte.
		*/
		.aux_sample_size = 1,
		};
		int fd;

		fd = sys_perf_event_open(&attr, -1, 0, -1, 0);
		/*
		* If the kernel attribute is big enough to contain aux_sample_size
		* then we assume that it is supported. We are relying on the kernel to
		* validate the attribute size before anything else that could be wrong.
		*/
		if (fd < 0 && errno == E2BIG)
		return false;
		if (fd >= 0)
		close(fd);

		return true;
		}

		void perf_evlist__config(struct evlist evlist, struct record_opts opts,
		struct callchain_param *callchain)
		{

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