[tip:perf/core] perf tools: Give user better message if precise is not supported

[tip-bot for David Ahern <dsahern@gmail.com>]

Commit-ID:  2305c82fb35dd2c8c9533303bb1693f1636c66e4
Gitweb:     http://git.kernel.org/tip/2305c82fb35dd2c8c9533303bb1693f1636c66e4
Author:     David Ahern <dsahern@gmail.com>
AuthorDate: Thu, 13 Sep 2012 14:59:15 -0600
Committer:  Arnaldo Carvalho de Melo <acme@redhat.com>
CommitDate: Wed, 24 Oct 2012 14:20:11 -0200

perf tools: Give user better message if precise is not supported

Platforms (e.g., VM's) without support for precise mode get a confusing
error message. e.g.,
$ 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.

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

which is not clear that precise mode might be the root problem. With this
patch:

$ perf record -e cycles:p -fo /tmp/perf.data -- sleep 1
  Error:
  'precise' request may not be supported. Try removing 'p' modifier
  sleep: Terminated

v2: softened message to 'may not be' supported per Robert's suggestion

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Robert Richter <robert.richter@amd.com>
Link: http://lkml.kernel.org/r/1347569955-54626-4-git-send-email-dsahern@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
---
 tools/perf/builtin-record.c |    5 +++++
 tools/perf/builtin-top.c    |    4 ++++
 2 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index 73b5d7f..53c9892 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -317,6 +317,11 @@ try_again:
 					  perf_evsel__name(pos));
 				rc = -err;
 				goto out;
+			} else if ((err == EOPNOTSUPP) && (attr->precise_ip)) {
+				ui__error("\'precise\' request may not be supported. "
+					  "Try removing 'p' modifier\n");
+				rc = -err;
+				goto out;
 			}
 
 			printf("\n");
diff --git a/tools/perf/builtin-top.c b/tools/perf/builtin-top.c
index fb9da71..f2ecd49 100644
--- a/tools/perf/builtin-top.c
+++ b/tools/perf/builtin-top.c
@@ -977,6 +977,10 @@ 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 == EOPNOTSUPP) && (attr->precise_ip)) {
+				ui__error("\'precise\' request may not be supported. "
+					  "Try removing 'p' modifier\n");
+				goto out_err;
 			}
 
 			ui__error("The sys_perf_event_open() syscall "