linux-kernel - Re: [PATCH V9 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE

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Message-ID: <20201020024925.GB13630@leoy-ThinkPad-X240s>
Date:   Tue, 20 Oct 2020 10:49:25 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Will Deacon <will@...nel.org>, kan.liang@...ux.intel.com,
        mingo@...hat.com, acme@...nel.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, alexander.shishkin@...ux.intel.com,
        jolsa@...hat.com, eranian@...gle.com, ak@...ux.intel.com,
        dave.hansen@...el.com, kirill.shutemov@...ux.intel.com,
        mpe@...erman.id.au, benh@...nel.crashing.org, paulus@...ba.org,
        David Miller <davem@...emloft.net>
Subject: Re: [PATCH V9 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE

On Fri, Oct 09, 2020 at 11:53:00AM +0200, Peter Zijlstra wrote:
> On Fri, Oct 09, 2020 at 10:37:51AM +0100, Will Deacon wrote:
> > On Fri, Oct 09, 2020 at 11:09:27AM +0200, Peter Zijlstra wrote:
> 
> > > Patch 4 makes it all far worse by exposing it to pretty much everybody.
> > > 
> > > Now, I think we can fix at least the user mappings with the below delta,
> > > but if archs are using non-page-table MMU sizes we'll need arch helpers.
> > > 
> > > ARM64 is in that last boat.
> > > 
> > > Will, can you live with the below, if not, what would you like to do,
> > > make the entire function __weak so that you can override it, or hook
> > > into it somewhere?
> > 
> > Hmm, so I don't think we currently have any PMUs that set 'data->addr'
> > on arm64, in which case maybe none of this currently matters for us.
> > 
> > However, I must admit that I couldn't figure out exactly what gets exposed
> > to userspace when the backend drivers don't look at the sample_type or
> > do anything with the addr field.
> 
> Patch 4:
> 
>   https://lkml.kernel.org/r/20201001135749.2804-5-kan.liang@linux.intel.com
> 
> is the one that exposes this to everybody with perf support. It will
> then report the page-size for the code address (SAMPLE_IP).

I can see there have another potentail customer to use page-size is
Arm SPE, but Arm SPE is hardware trace based sample but not interrupt
based sample.  For this case, I think this patch set cannot be
directly applied to the AUX trace data.

Thanks,
Leo