Re: [PATCH v2 10/13] perf record: Lazy load kernel symbols

[Adrian Hunter]

On 12/10/23 09:23, Ian Rogers wrote:
> Commit 5b7ba82a7591 ("perf symbols: Load kernel maps before using")
> changed it so that loading a kernel dso would cause the symbols for
> the dso to be eagerly loaded. For perf record this is overhead as the
> symbols won't be used. Add a symbol_conf to control the behavior and
> disable it for perf record and perf inject.
> 
> Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
> ---
>  tools/perf/builtin-inject.c   | 4 ++++
>  tools/perf/builtin-record.c   | 2 ++
>  tools/perf/util/event.c       | 4 ++--
>  tools/perf/util/symbol_conf.h | 3 ++-
>  4 files changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/perf/builtin-inject.c b/tools/perf/builtin-inject.c
> index c8cf2fdd9cff..1539fb18c749 100644
> --- a/tools/perf/builtin-inject.c
> +++ b/tools/perf/builtin-inject.c
> @@ -2265,6 +2265,10 @@ int cmd_inject(int argc, const char **argv)
>  		"perf inject [<options>]",
>  		NULL
>  	};
> +
> +	/* Disable eager loading of kernel symbols that adds overhead to perf inject. */
> +	symbol_conf.lazy_load_kernel_maps = true;

Possibly not for itrace kernel decoding, so:

	if (!inject->itrace_synth_opts.set)
		symbol_conf.lazy_load_kernel_maps = true;

> +
>  #ifndef HAVE_JITDUMP
>  	set_option_nobuild(options, 'j', "jit", "NO_LIBELF=1", true);
>  #endif
> diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
> index dcf288a4fb9a..8ec818568662 100644
> --- a/tools/perf/builtin-record.c
> +++ b/tools/perf/builtin-record.c
> @@ -3989,6 +3989,8 @@ int cmd_record(int argc, const char **argv)
>  # undef set_nobuild
>  #endif
>  
> +	/* Disable eager loading of kernel symbols that adds overhead to perf record. */
> +	symbol_conf.lazy_load_kernel_maps = true;
>  	rec->opts.affinity = PERF_AFFINITY_SYS;
>  
>  	rec->evlist = evlist__new();
> diff --git a/tools/perf/util/event.c b/tools/perf/util/event.c
> index 923c0fb15122..68f45e9e63b6 100644
> --- a/tools/perf/util/event.c
> +++ b/tools/perf/util/event.c
> @@ -617,13 +617,13 @@ struct map *thread__find_map(struct thread *thread, u8 cpumode, u64 addr,
>  	if (cpumode == PERF_RECORD_MISC_KERNEL && perf_host) {
>  		al->level = 'k';
>  		maps = machine__kernel_maps(machine);
> -		load_map = true;
> +		load_map = !symbol_conf.lazy_load_kernel_maps;
>  	} else if (cpumode == PERF_RECORD_MISC_USER && perf_host) {
>  		al->level = '.';
>  	} else if (cpumode == PERF_RECORD_MISC_GUEST_KERNEL && perf_guest) {
>  		al->level = 'g';
>  		maps = machine__kernel_maps(machine);
> -		load_map = true;
> +		load_map = !symbol_conf.lazy_load_kernel_maps;
>  	} else if (cpumode == PERF_RECORD_MISC_GUEST_USER && perf_guest) {
>  		al->level = 'u';
>  	} else {
> diff --git a/tools/perf/util/symbol_conf.h b/tools/perf/util/symbol_conf.h
> index 0b589570d1d0..2b2fb9e224b0 100644
> --- a/tools/perf/util/symbol_conf.h
> +++ b/tools/perf/util/symbol_conf.h
> @@ -42,7 +42,8 @@ struct symbol_conf {
>  			inline_name,
>  			disable_add2line_warn,
>  			buildid_mmap2,
> -			guest_code;
> +			guest_code,
> +			lazy_load_kernel_maps;
>  	const char	*vmlinux_name,
>  			*kallsyms_name,
>  			*source_prefix,