linux-kernel - Re: [PATCH V6] perf: Add PERF_SAMPLE_PHYS

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Message-ID: <CABPqkBSeYKjZ9eKzrALFcv8gHJ2RWQaBntkpe2Fk5=mznDCs+A@mail.gmail.com>
Date:   Wed, 23 Aug 2017 10:00:37 -0700
From:   Stephane Eranian <eranian@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     "Liang, Kan" <kan.liang@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>
Subject: Re: [PATCH V6] perf: Add PERF_SAMPLE_PHYS_ADDR

On Wed, Aug 23, 2017 at 7:39 AM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Wed, Aug 23, 2017 at 04:33:08PM +0200, Peter Zijlstra wrote:
>> > @@ -6145,6 +6183,9 @@ void perf_prepare_sample(struct perf_event_header *header,
>> >
>> >             header->size += size;
>> >     }
>> > +
>> > +   if (sample_type & PERF_SAMPLE_PHYS_ADDR)
>> > +           data->phys_addr = perf_virt_to_phys(data->addr);
>>
>> Only problem with this now is that it requires SAMPLE_ADDR to also be
>> set in order to obtain data->addr.
>>
>> Either fix all to set data->attr for (SAMPLE_ADDR || SAMPLE_PHYS_ADDR)
>> or mandate SAMPLE_ADDR when SAMPLE_PHYS_ADDR.
>
> I think the former suggestion is better, as it allows for smaller
> samples.

Agreed. I may only care about physical addresses, so SAMPLE_PHYS_ADDR
should suffice from the user.
The kernel must save the virtual address in data->addr, and then convert it.