From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Vince Weaver <vincent.weaver@maine.edu>,
Paul Mackerras <paulus@samba.org>,
Martin Schwidefsky <schwidefsky@de.ibm.com>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org
Subject: Re: [PATCH 1/2] perf: return ENOENT instead of ENOTSUPP
Date: Thu, 11 Jun 2015 12:25:01 +0200 [thread overview]
Message-ID: <1434018301.1495.73.camel@twins> (raw)
In-Reply-To: <1434016745-17608-1-git-send-email-brueckner@linux.vnet.ibm.com>
On Thu, 2015-06-11 at 11:59 +0200, Hendrik Brueckner wrote:
> The ENOTSUPP (which actually should be EOPNOTSUPP for user space) does not
> trigger a fallback event selection, for example, by perf record.
> If hardware support for the cycles perf event is available, but the hardware
> does not provide interrupts, returning ENOTSUPP causes perf to end. Returning
> ENOENT causes the perf tool to fallback to a software-based cycle PMU that
> supports interrupts.
>
> The commit 53b25335dd ("perf: Disable sampled events if no PMU interrupt")
> introduced that incompatible change.
That's 3.16
> if (event->pmu->capabilities & PERF_PMU_CAP_NO_INTERRUPT) {
> - err = -ENOTSUPP;
> + err = -ENOENT;
> goto err_alloc;
> }
> }
And now you would be changing an API that's been around for at least 4
releases.
Also, I really think -ENOENT is the wrong return here, you're asking for
things that's not supported, not for something that's not there.
next prev parent reply other threads:[~2015-06-11 10:25 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-11 9:59 [PATCH 1/2] perf: return ENOENT instead of ENOTSUPP Hendrik Brueckner
2015-06-11 9:59 ` [PATCH 2/2] perf: correct event accounting imbalance on error path Hendrik Brueckner
2015-06-11 10:25 ` Peter Zijlstra [this message]
2015-06-11 13:02 ` [PATCH 1/2] perf: return ENOENT instead of ENOTSUPP Hendrik Brueckner
2015-06-11 13:28 ` Peter Zijlstra
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