linux-kernel - RE: [PATCH V3 14/14] coresight: etm-perf: Add support for trace buffer format

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Message-ID: <DB7PR08MB3355B1A444324DBC5AF8003C86BB0@DB7PR08MB3355.eurprd08.prod.outlook.com>
Date:   Wed, 27 Jan 2021 13:00:37 +0000
From:   Al Grant <Al.Grant@....com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Anshuman Khandual <Anshuman.Khandual@....com>
CC:     "coresight@...ts.linaro.org" <coresight@...ts.linaro.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "lcherian@...vell.com" <lcherian@...vell.com>,
        "mike.leach@...aro.org" <mike.leach@...aro.org>
Subject: RE: [PATCH V3 14/14] coresight: etm-perf: Add support for trace
 buffer format

> > +/* CoreSight PMU AUX buffer formats */
> > +#define PERF_AUX_FLAG_CORESIGHT_FORMAT_CORESIGHT	0x0000 /*
> Default for backward compatibility */
> > +#define PERF_AUX_FLAG_CORESIGHT_FORMAT_RAW		0x0100 /*
> Raw format of the source */
> 
> Would CORESIGHT_FORMAT_ETR / CORESIGHT_FORMAT_TRBE be better
> names?

Unformatted (raw) streams could be used any time you had a writer dedicated
to a single trace source. So in a situation where you had one ETR per CPU,
it would be appropriate to use an unformatted stream. A TRBE is always
dedicated to a single CPU, but potentially you (i.e. when designing the system)
can do this with any type of trace sink. So the raw/formatted distinction is
really about whether you are combining multiple streams in one buffer or not,
rather than the type of block that is writing into the buffer.

Al