linux-kernel - Re: [PATCH] perf, record: Add clockid parameter

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Message-ID: <20150327201534.GD6291@redhat.com>
Date:	Fri, 27 Mar 2015 17:15:34 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, tglx@...utronix.de,
	jolsa@...hat.com, eranian@...gle.com,
	torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
	john.stultz@...aro.org, hpa@...or.com, akpm@...ux-foundation.org,
	mingo@...nel.org
Subject: Re: [PATCH] perf, record: Add clockid parameter

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

- Arnaldo
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