Date: Wed, 12 Jul 2017 09:57:11 +0200
From: Ingo Molnar <mingo@kernel.org>
To: "Jin, Yao" <yao.jin@linux.intel.com>
Cc: Kyle Huey <me@kylehuey.com>, Mark Rutland <mark.rutland@arm.com>,
        gregkh@linuxfoundation.org, Peter Zijlstra <peterz@infradead.org>,
        Vince Weaver <vincent.weaver@maine.edu>, stable@vger.kernel.org,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Arnaldo Carvalho de Melo <acme@redhat.com>,
        Jiri Olsa <jolsa@redhat.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Namhyung Kim <namhyung@kernel.org>,
        Stephane Eranian <eranian@google.com>,
        Thomas Gleixner <tglx@linutronix.de>, acme@kernel.org,
        jolsa@kernel.org, kan.liang@intel.com,
        Will Deacon <will.deacon@arm.com>,
        open list <linux-kernel@vger.kernel.org>,
        "Robert O'Callahan" <robert@ocallahan.org>
Subject: Re: [PATCH] perf/core: generate overflow signal when samples are
 dropped (WAS: Re: [REGRESSION] perf/core: PMU interrupts dropped if we
 entered the kernel in the "skid" region)
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* Jin, Yao <yao.jin@linux.intel.com> wrote:

> Could we provide 2 options in user space when enabling the event sampling?
> 
> One option is for the use case like rr debugger which only cares the PMI 
> interrupt but doesn't care the skid. The skid samples doesn't need to be 
> dropped.

Since it's an information leak, this is not something we want to expose as an 
interface. It's also a very ugly interface: why not just *clear* the sample, 
instead of dropping it?

The hardware messed up and gave us something we specifically did not permit 
user-space to collect. We have to fix the bad effects to the best extent we can, 
and not based on some knob.

Thanks,

	Ingo