linux-kernel - [PATCH 2/2] perf tools: Skip read of kernel maps once it failed

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Date:   Fri, 19 Jan 2018 17:11:03 +0100
From:   Jiri Olsa <jolsa@...nel.org>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: [PATCH 2/2] perf tools: Skip read of kernel maps once it failed

Current perf report is real slow on newer kernels,
with following commit:
  c0f3ea158939 ("stop using '%pK' for /proc/kallsyms pointer values")

which prevent pointers in /proc/kallsyms, in case
kernel.perf_event_paranoid=2.

That makes perf to fail in finding kernel map details,
and keep parsing it again for every kernel sample.

Adding and setting a new machine::vmlinux_maps_failed
flag after first failed parsing attempt and using it
to prevent new pointless parsing.

TODO We might want to add some perf report warning
about that.

Link: http://lkml.kernel.org/n/tip-ld2kp994rhz6i341igt8f98y@git.kernel.org
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 tools/perf/util/machine.c | 6 ++++--
 tools/perf/util/machine.h | 1 +
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index b05a67464c03..5e9648817077 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1222,13 +1222,15 @@ int machine__create_kernel_maps(struct machine *machine)
 	u64 addr = 0;
 	int ret;
 
-	if (kernel == NULL)
+	if (kernel == NULL || machine->vmlinux_maps_failed)
 		return -1;
 
 	ret = __machine__create_kernel_maps(machine, kernel);
 	dso__put(kernel);
-	if (ret < 0)
+	if (ret < 0) {
+		machine->vmlinux_maps_failed = true;
 		return -1;
+	}
 
 	if (symbol_conf.use_modules && machine__create_modules(machine) < 0) {
 		if (machine__is_host(machine))
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index 5ce860b64c74..edcb007333cb 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -42,6 +42,7 @@ struct machine {
 	u16		  id_hdr_size;
 	bool		  comm_exec;
 	bool		  kptr_restrict_warned;
+	bool		  vmlinux_maps_failed;
 	char		  *root_dir;
 	struct threads    threads[THREADS__TABLE_SIZE];
 	struct vdso_info  *vdso_info;
-- 
2.13.6