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Date: Mon, 3 Jul 2017 18:22:28 +0200
From: Jiri Olsa <jolsa@redhat.com>
To: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>, lkml <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Namhyung Kim <namhyung@kernel.org>, David Ahern <dsahern@gmail.com>,
        Thomas Richter <tmricht@linux.vnet.ibm.com>
Subject: Re: [PATCHv2 01/15] perf tools: Fix -n option
Message-ID: <20170703162228.GA22468@krava>
References: <20170703145030.12903-1-jolsa@kernel.org>
 <20170703145030.12903-2-jolsa@kernel.org>
 <20170703145739.GA16278@kernel.org>
 <20170703151654.GA16010@krava>
 <20170703161003.GB16278@kernel.org>
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On Mon, Jul 03, 2017 at 01:10:04PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Jul 03, 2017 at 05:16:54PM +0200, Jiri Olsa escreveu:
> > On Mon, Jul 03, 2017 at 11:57:39AM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Mon, Jul 03, 2017 at 04:50:16PM +0200, Jiri Olsa escreveu:
> > > > The kernel fails to add a non sampling event event
> > > > with having precise_ip set.
> > > > 
> > > > Make sure the precise_ip is 0 when using -n option
> > > > to create non sampling event in record.
> > > 
> > > Ok, but how could that happen? What was the scenario? Which command? Can
> > > you provide a command line that causes the problem?
> > 
> > [jolsa@krava perf]$ ./perf record -e cycles:ppp -n ls
> > Lowering default frequency rate to 3000.
> > Please consider tweaking /proc/sys/kernel/perf_event_max_sample_rate.
> > Error:
> > The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cycles:pppu).
> > /bin/dmesg may provide additional information.
> > No CONFIG_PERF_EVENTS=y kernel support configured?
> > 
> > v2 attached, thanks
> 
> Ok, so the user asks for --no-samples but at the same time asks for
> precision equal to :ppp, we should stop right there and warn the user
> that that is not possible, instead of silently dropping off what the
> user explicitely asked.

well I take this option more like debug/devel one.. you have
failing command line and want to investigate the kernel state
without having samples generated under your fingers

can't see why would normal user need it

> 
> I'm cooking a few patches to allow that, then we can apply your patch,
> that, with the current set of users will never kick in :-)


ok

jirka