linux-kernel - Re: [PATCH V7 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE

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Date:   Thu, 17 Sep 2020 15:02:58 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Liang, Kan" <kan.liang@...ux.intel.com>, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, linux-kernel@...r.kernel.org
Cc:     mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, eranian@...gle.com, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com, mpe@...erman.id.au,
        benh@...nel.crashing.org, paulus@...ba.org
Subject: Re: [PATCH V7 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE

On 9/17/20 2:58 PM, Liang, Kan wrote:
> The user space perf tool looks like a better place for this kind of
> warning. The perf tool knows the total number of the samples. It also
> knows the number of the page size 0 samples. We can set a threshold,
> e.g., 90%. If 90% of the samples have the page size 0, perf tool will
> throw out a warning message.

Sounds good to me.

> The problem is that the warning from the perf tool usually includes some
> hints regarding the cause of the warning or possible solution to
> workaround/fix the warning. What message should we deliver to the users?
> "Warning: Too many error page size. Address space isolation feature may
> be enabled, please check"?

That's not particularly actionable for an end user.  Do any of the perf
errors just tell them to submit a bug report?  "Excessive number of page
size lookup errors, please report to..."