linux-kernel - Re: [PATCH 03/24] perf: Add build id data in mmap2 event

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Date:   Tue, 10 Nov 2020 09:28:51 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Michael Petlan <mpetlan@...hat.com>,
        Song Liu <songliubraving@...com>,
        Ian Rogers <irogers@...gle.com>,
        Stephane Eranian <eranian@...gle.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 03/24] perf: Add build id data in mmap2 event

On Mon, Nov 09, 2020 at 10:53:54PM +0100, Jiri Olsa wrote:
> There's new misc bit for mmap2 to signal there's build
> id data in it:
> 
>   #define PERF_RECORD_MISC_BUILD_ID              (1 << 14)

PERF_RECORD_MISC_MMAP_BUILD_ID would be consistent with the existing
PERF_RECORD_MISC_MMAP_DATA naming.

Also, AFAICT there's still a bunch of unused bits in misc.

	012	    CDEF
	|||---------||||

Where:
	0-2	CPUMODE_MASK

	C	PROC_MAP_PARSE_TIMEOUT
	D	MMAP_DATA / COMM_EXEC / FORK_EXEC / SWITCH_OUT
	E	EXACT_IP / SCHED_OUT_PREEMPT
	F	(reserved)

Maybe we should put in a comment to keep track of the hole ?

Also, perhaps it is time to use F to indicate that @size is in 8 instead
of 1 ? That would increase our max entry size to 512K, people seem to
hit his 64K limit (insane as it is).