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

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Message-Id: <20231012062359.1616786-11-irogers@google.com>
Date:   Wed, 11 Oct 2023 23:23:56 -0700
From:   Ian Rogers <irogers@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Nick Terrell <terrelln@...com>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Song Liu <song@...nel.org>,
        Sandipan Das <sandipan.das@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        James Clark <james.clark@....com>,
        Liam Howlett <liam.howlett@...cle.com>,
        Miguel Ojeda <ojeda@...nel.org>, Leo Yan <leo.yan@...aro.org>,
        German Gomez <german.gomez@....com>,
        Ravi Bangoria <ravi.bangoria@....com>,
        Artem Savkov <asavkov@...hat.com>,
        Athira Rajeev <atrajeev@...ux.vnet.ibm.com>,
        Andi Kleen <ak@...ux.intel.com>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org, bpf@...r.kernel.org
Subject: [PATCH v2 10/13] perf record: Lazy load kernel symbols

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@...gle.com>
---
 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;
+
 #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,
-- 
2.42.0.609.gbb76f46606-goog