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

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Date:	Fri, 27 Mar 2015 11:35:25 -0600
From:	David Ahern <dsahern@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	tglx@...utronix.de, acme@...hat.com, 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

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.

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