linux-kernel - Re: [PATCH 3/4] perf record: Save DSO build-ID for synthesizing

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Date:   Tue, 20 Sep 2022 16:59:59 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Namhyung Kim <namhyung@...nel.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ian Rogers <irogers@...gle.com>,
        linux-perf-users@...r.kernel.org
Subject: Re: [PATCH 3/4] perf record: Save DSO build-ID for synthesizing

On 16/09/22 20:59, Namhyung Kim wrote:
> When synthesizing MMAP2 with build-id, it'd read the same file repeatedly as
> it has no idea if it's done already.  Maintain a dsos to check that and skip
> the file access if possible.
> 
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
>  tools/perf/util/synthetic-events.c | 49 +++++++++++++++++++++++++-----
>  1 file changed, 42 insertions(+), 7 deletions(-)
> 
> diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c
> index 9d4f5dacd154..e6978b2dee8f 100644
> --- a/tools/perf/util/synthetic-events.c
> +++ b/tools/perf/util/synthetic-events.c
> @@ -4,6 +4,7 @@
>  #include "util/data.h"
>  #include "util/debug.h"
>  #include "util/dso.h"
> +#include "util/dsos.h"
>  #include "util/event.h"
>  #include "util/evlist.h"
>  #include "util/machine.h"
> @@ -47,12 +48,25 @@
>  
>  unsigned int proc_map_timeout = DEFAULT_PROC_MAP_PARSE_TIMEOUT;
>  
> +static bool synth_init_done;
> +static struct dsos synth_dsos;
> +
>  void perf_event__synthesize_start(void)
>  {
> +	if (synth_init_done)
> +		return;
> +
> +	dsos__init(&synth_dsos);
> +
> +	synth_init_done = true;
>  }
>  
>  void perf_event__synthesize_stop(void)
>  {
> +	if (!synth_init_done)
> +		return;
> +
> +	dsos__exit(&synth_dsos);
>  }
>  
>  int perf_tool__process_synth_event(struct perf_tool *tool,
> @@ -374,26 +388,47 @@ static bool read_proc_maps_line(struct io *io, __u64 *start, __u64 *end,
>  static void perf_record_mmap2__read_build_id(struct perf_record_mmap2 *event,
>  					     bool is_kernel)
>  {
> -	struct build_id bid;
> +	struct build_id _bid, *bid = &_bid;
> +	struct dso *dso = NULL;
> +	struct dso_id id;
>  	int rc;
>  
> -	if (is_kernel)
> -		rc = sysfs__read_build_id("/sys/kernel/notes", &bid);
> -	else
> -		rc = filename__read_build_id(event->filename, &bid) > 0 ? 0 : -1;
> +	if (is_kernel) {
> +		rc = sysfs__read_build_id("/sys/kernel/notes", bid);
> +		goto out;
> +	}
> +
> +	id.maj = event->maj;
> +	id.min = event->min;
> +	id.ino = event->ino;
> +	id.ino_generation = event->ino_generation;
>  

There might be some paths missing perf_event__synthesize_start()
e.g. perf trace
So it would probably be safer to use lazy initialization for
synth_dsos.

Also, callers of perf_record_mmap2__read_build_id() have a struct
machine so I wonder about putting synth_dsos in struct machine ?
Or even just using machine->dsos ?

> +	dso = dsos__findnew_id(&synth_dsos, event->filename, &id);
> +	if (dso && dso->has_build_id) {
> +		bid = &dso->bid;
> +		rc = 0;
> +		goto out;
> +	}
> +
> +	rc = filename__read_build_id(event->filename, bid) > 0 ? 0 : -1;
> +
> +out:
>  	if (rc == 0) {
> -		memcpy(event->build_id, bid.data, sizeof(bid.data));
> -		event->build_id_size = (u8) bid.size;
> +		memcpy(event->build_id, bid->data, sizeof(bid->data));
> +		event->build_id_size = (u8) bid->size;
>  		event->header.misc |= PERF_RECORD_MISC_MMAP_BUILD_ID;
>  		event->__reserved_1 = 0;
>  		event->__reserved_2 = 0;
> +
> +		if (dso && !dso->has_build_id)
> +			dso__set_build_id(dso, bid);
>  	} else {
>  		if (event->filename[0] == '/') {
>  			pr_debug2("Failed to read build ID for %s\n",
>  				  event->filename);
>  		}
>  	}
> +	dso__put(dso);
>  }
>  
>  int perf_event__synthesize_mmap_events(struct perf_tool *tool,