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SubjectRe: [PATCH 10/11] perf tool: give user better message if precise is not supported
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Hi, David

On Fri, 20 Jul 2012 17:25:55 -0600, David Ahern wrote:
> 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
>

The name 'PEBS' is intel-specific, so shouldn't we try to avoid using it
directly? How about this:

Precise event sampling is not supported. Try removing 'p' modifier

Thanks,
Namhyung


> Signed-off-by: David Ahern <dsahern@gmail.com>
> Cc: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Jiri Olsa <jolsa@redhat.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.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 "


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