Re: [PATCH] perf, record: Add clockid parameter

From: Stephane Eranian <eranian@google.com>
To: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Jiri Olsa <jolsa@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	LKML <linux-kernel@vger.kernel.org>,
	John Stultz <john.stultz@linaro.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Ingo Molnar <mingo@kernel.org>
Subject: Re: [PATCH] perf, record: Add clockid parameter
Date: Fri, 27 Mar 2015 16:07:01 -0700	[thread overview]
Message-ID: <CABPqkBTOUc-aB=hp7pu37z50+QHRHRXWP3wdLtePScqic7P1Dg@mail.gmail.com> (raw)
In-Reply-To: <20150327201534.GD6291@redhat.com>

On Fri, Mar 27, 2015 at 1:15 PM, Arnaldo Carvalho de Melo
<acme@redhat.com> wrote:
> Em Fri, Mar 27, 2015 at 11:35:25AM -0600, David Ahern escreveu:
>> On 3/27/15 11:20 AM, Peter Zijlstra wrote:
>> >>This is a new feature which means use_clockid on older kernels will fail. So
>> >>need to catch that and throw an error -- perhaps yet another probe function.
>
>> >How does that work? What do I grep to find an example? I figured if the
>> >kernel didn't support the syscall will fail and we'll terminate
>> >someplace.
>
>> Look at __perf_evsel__open(). In this case you probably do not want
>> to fallback but tell the user the clock id option is not supported.
>> The problem is deciphering the failure is due to the clock id versus
>> all the other failure reasons.
>
> I.e. we're back to the sys_perf_event_open() error reporting suckz rockz
> thing, this time with PeterZ trying to find a way to avoid getting back
> to that discussion... /me runz... ;-P
>
Why not have the kernel advertise the perf capabilities (in procfs or
sysfs) instead this
guessing game with the return values?