linux-kernel - [PATCH] Increase MAX_NR_CPUS and MAX

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Date:   Thu, 20 Jun 2019 13:55:28 -0500
From:   Kyle Meyer <meyerk@....com>
To:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org
Cc:     Kyle Meyer <kyle.meyer@....com>
Subject: [PATCH] Increase MAX_NR_CPUS and MAX_CACHES

From: Kyle Meyer <kyle.meyer@....com>

Attempting to profile 1024 or more CPUs with perf causes two errors:

perf record -a
[ perf record: Woken up X times to write data ]
way too many cpu caches..
[ perf record: Captured and wrote X MB perf.data (X samples) ]

perf report -C 1024
Error: failed to set  cpu bitmap
Requested CPU 1024 too large. Consider raising MAX_NR_CPUS

Increasing MAX_NR_CPUS from 1024 to 2048 and redefining MAX_CACHES as
MAX_NR_CPUS * 4 returns normal functionality to perf:

perf record -a
[ perf record: Woken up X times to write data ]
[ perf record: Captured and wrote X MB perf.data (X samples) ]

perf report -C 1024
...
---
 samples/bpf/map_perf_test_kern.c | 2 +-
 samples/bpf/map_perf_test_user.c | 2 +-
 tools/perf/perf.h                | 2 +-
 tools/perf/util/header.c         | 2 +-
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/samples/bpf/map_perf_test_kern.c b/samples/bpf/map_perf_test_kern.c
index 2b2ffb97018b..342738a1e386 100644
--- a/samples/bpf/map_perf_test_kern.c
+++ b/samples/bpf/map_perf_test_kern.c
@@ -11,7 +11,7 @@
 #include "bpf_helpers.h"
 
 #define MAX_ENTRIES 1000
-#define MAX_NR_CPUS 1024
+#define MAX_NR_CPUS 2048
 
 struct bpf_map_def SEC("maps") hash_map = {
 	.type = BPF_MAP_TYPE_HASH,
diff --git a/samples/bpf/map_perf_test_user.c b/samples/bpf/map_perf_test_user.c
index fe5564bff39b..da3c101ca776 100644
--- a/samples/bpf/map_perf_test_user.c
+++ b/samples/bpf/map_perf_test_user.c
@@ -22,7 +22,7 @@
 #include "bpf_load.h"
 
 #define TEST_BIT(t) (1U << (t))
-#define MAX_NR_CPUS 1024
+#define MAX_NR_CPUS 2048
 
 static __u64 time_get_ns(void)
 {
diff --git a/tools/perf/perf.h b/tools/perf/perf.h
index 711e009381ec..74d0124d38f3 100644
--- a/tools/perf/perf.h
+++ b/tools/perf/perf.h
@@ -26,7 +26,7 @@ static inline unsigned long long rdclock(void)
 }
 
 #ifndef MAX_NR_CPUS
-#define MAX_NR_CPUS			1024
+#define MAX_NR_CPUS			2048
 #endif
 
 extern const char *input_name;
diff --git a/tools/perf/util/header.c b/tools/perf/util/header.c
index 06ddb6618ef3..bf017901f75c 100644
--- a/tools/perf/util/header.c
+++ b/tools/perf/util/header.c
@@ -1121,7 +1121,7 @@ static int build_caches(struct cpu_cache_level caches[], u32 size, u32 *cntp)
 	return 0;
 }
 
-#define MAX_CACHES 2000
+#define MAX_CACHES MAX_NR_CPUS * 4
 
 static int write_cache(struct feat_fd *ff,
 		       struct perf_evlist *evlist __maybe_unused)
-- 
2.20.1