linux-kernel - Re: [RFC PATCH] perf: Handle multiple formatted AUX records

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Message-ID: <YA6lJPG7DGnlL8yh@hirez.programming.kicks-ass.net>
Date:   Mon, 25 Jan 2021 12:01:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
        Ingo Molnar <mingo@...hat.com>, will@...nel.org,
        mark.rutland@....com, mike.leach@...aro.org, al.grant@....com,
        anshuman.khandual@....com, mathieu.poirier@...aro.org,
        linux-arm-kernel@...ts.infradead.org, jolsa@...hat.com,
        acme@...nel.org
Subject: Re: [RFC PATCH] perf: Handle multiple formatted AUX records

On Mon, Jan 25, 2021 at 10:45:06AM +0000, Suzuki K Poulose wrote:
> On 1/25/21 10:25 AM, Peter Zijlstra wrote:

> > Since we have a whole u64, do we want to reserve a whole nibble (or
> > maybe even a byte) for a format type? Because with a single bit like
> > this, we'll kick ourselves when we end up with the need for a 3rd format
> > type.
> > 
> 
> Sure, makes sense. We could do:
> 
> #define PERF_AUX_FLAG_PMU_FORMAT_TYPE_MASK	0xff00
> 
> Additionally, the values could be allocated by individual PMUs and
> interpreted by the corresponding counterpart. That way we don't
> have to worry about centralized allocation of the "TYPE" fields.
> 
> e,g:
> 
> #define PERF_AUX_FLAG_CORESIGHT_FORMAT_CORESIGHT	0x0000
> #define PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW		0x0100
> 
> #define PERF_AUX_FLAG_RANDOM_PMU_FORMAT_FMT1		0x0000
> #define PERF_AUX_FLAG_RANDOM_PMU_FORMAT_FMT2		0x0100
> 
> 
> What do you think ?

Sounds good to me.