From: Jiri Olsa <jolsa@redhat.com>
To: Ian Rogers <irogers@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Namhyung Kim <namhyung@kernel.org>,
linux-kernel@vger.kernel.org,
Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH] perf stat: force error in fallback on :k events
Date: Tue, 14 Apr 2020 15:02:09 +0200 [thread overview]
Message-ID: <20200414130209.GD117177@krava> (raw)
In-Reply-To: <20200413235515.221467-1-irogers@google.com>
On Mon, Apr 13, 2020 at 04:55:15PM -0700, Ian Rogers wrote:
> From: Stephane Eranian <eranian@google.com>
>
> When it is not possible for a non-privilege perf command
> to monitor at the kernel level (:k), the fallback code forces
> a :u. That works if the event was previously monitoring both levels.
> But if the event was already constrained to kernel only, then it does
> not make sense to restrict it to user only.
> Given the code works by exclusion, a kernel only event would have:
> attr->exclude_user = 1
> The fallback code would add:
> attr->exclude_kernel = 1;
>
> In the end the end would not monitor in either the user level or kernel
> level. In other words, it would count nothing.
>
> An event programmed to monitor kernel only cannot be switched to user only
> without seriously warning the user.
>
> This patch forces an error in this case to make it clear the request
> cannot really be satisfied.
>
> Signed-off-by: Stephane Eranian <eranian@google.com>
> Reviewed-by: Ian Rogers <irogers@google.com>
> ---
> tools/perf/util/evsel.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
> index d23db6755f51..d1e8862b86ce 100644
> --- a/tools/perf/util/evsel.c
> +++ b/tools/perf/util/evsel.c
> @@ -2446,6 +2446,13 @@ bool perf_evsel__fallback(struct evsel *evsel, int err,
> char *new_name;
> const char *sep = ":";
>
> + if (evsel->core.attr.exclude_user) {
> + scnprintf(msg, msgsize,
> +"kernel.perf_event_paranoid=%d, event set to exclude user, so cannot also exclude kernel",
> + paranoid);
> + return false;
I'm not able to get this error printed, it seems to be
overwritten by perf_evsel__open_strerror call
please include perf example with the new output
thanks,
jirka
> + }
> +
> /* Is there already the separator in the name. */
> if (strchr(name, '/') ||
> strchr(name, ':'))
> --
> 2.26.0.110.g2183baf09c-goog
>
next prev parent reply other threads:[~2020-04-14 13:03 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-13 23:55 [PATCH] perf stat: force error in fallback on :k events Ian Rogers
2020-04-14 13:02 ` Jiri Olsa [this message]
2020-04-14 14:38 ` Ian Rogers
2020-04-14 15:12 ` Jiri Olsa
2020-04-14 16:21 ` Ian Rogers
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