linux-kernel - [PATCH 10/11] perf tool: give user better message if precise is not supported

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Date:	Fri, 20 Jul 2012 17:25:55 -0600
From:	David Ahern <dsahern@...il.com>
To:	acme@...stprotocols.net, linux-kernel@...r.kernel.org
Cc:	David Ahern <dsahern@...il.com>, Ingo Molnar <mingo@...nel.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Namhyung Kim <namhyung@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH 10/11] perf tool: give user better message if precise is not supported

If the PEBS is not supported (e.g., a VM) and the precise modifier is
set the user is given a confusing error message:

  $ perf top -e cycles:p

  The sys_perf_event_open() syscall returned with 95 (Operation not supported).
/bin/dmesg may provide additional information.
  No CONFIG_PERF_EVENTS=y kernel support configured?

  $ perf record -e cycles:p -a -- sleep 1

  Error: sys_perf_event_open() syscall returned with 95 (Operation not
supported).  /bin/dmesg may provide additional information.

  Fatal: No hardware sampling interrupt available. No APIC? If so then you can
boot the kernel with the "lapic" boot parameter to force-enable it.

Which in no way conveys the real error. With this patch:
  $ perf top -e cycles:p
  PEBS request not supported. Try removing 'p' modifier

  $ perf record -e cycles:p -a -- sleep 1
  PEBS request not supported. Try removing 'p' modifier

Signed-off-by: David Ahern <dsahern@...il.com>
Cc: Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Jiri Olsa <jolsa@...hat.com>
Cc: Namhyung Kim <namhyung@...nel.org>
Cc: Frederic Weisbecker <fweisbec@...il.com>
Cc: Peter Zijlstra <peterz@...radead.org>
---
 tools/perf/builtin-record.c |    4 ++++
 tools/perf/builtin-top.c    |    4 ++++
 2 files changed, 8 insertions(+)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index f5a6452..911e300 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -267,6 +267,10 @@ try_again:
 				ui__error("The %s event is not supported.\n",
 					  perf_evsel__name(pos));
 				exit(EXIT_FAILURE);
+			} else if ((err == ENOTSUP) && (attr->precise_ip)) {
+				ui__error("PEBS request not supported. "
+					  "Try removing 'p' modifier\n");
+				exit(EXIT_FAILURE);
 			}
 
 			printf("\n");
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index 0ce665c..1706dc9 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -968,6 +968,10 @@ try_again:
 				ui__error("Too many events are opened.\n"
 					    "Try again after reducing the number of events\n");
 				goto out_err;
+			} else if ((err == ENOTSUP) && (attr->precise_ip)) {
+				ui__error("PEBS request not supported. "
+					    "Try removing 'p' modifier\n");
+				goto out_err;
 			}
 
 			ui__error("The sys_perf_event_open() syscall "
-- 
1.7.10.1

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