[PATCH 27/31] perf tools: Pass available CPU number to clang compiler

[Wang Nan <wangnan0@huawei.com>]

This patch introduces a new macro "__NR_CPUS__" to perf's embedded
clang compiler, which represent the available CPU counters in this
system. BPF program can use this macro to create a map with same
number of system CPUs. For exmaple:

 struct bpf_map_def SEC("maps") pmu_map = {
     .type = BPF_MAP_TYPE_PERF_EVENT_ARRAY,
     .key_size = sizeof(int),
     .value_size = sizeof(u32),
     .max_entries = __NR_CPUS__,
 };

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/n/ebpf-y603iy62s8w4br4t2gxfois4@git.kernel.org
---
 tools/perf/util/llvm-utils.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/tools/perf/util/llvm-utils.c b/tools/perf/util/llvm-utils.c
index 4f6a478..80eecef 100644
--- a/tools/perf/util/llvm-utils.c
+++ b/tools/perf/util/llvm-utils.c
@@ -11,10 +11,11 @@
 #include "cache.h"
 
 #define CLANG_BPF_CMD_DEFAULT_TEMPLATE				\
-		"$CLANG_EXEC -D__KERNEL__ $CLANG_OPTIONS "	\
-		"$KERNEL_INC_OPTIONS -Wno-unused-value "	\
-		"-Wno-pointer-sign -working-directory "		\
-		"$WORKING_DIR -c \"$CLANG_SOURCE\" -target bpf -O2 -o -"
+		"$CLANG_EXEC -D__KERNEL__ -D__NR_CPUS__=$NR_CPUS "\
+		"$CLANG_OPTIONS $KERNEL_INC_OPTIONS "		\
+		"-Wno-unused-value -Wno-pointer-sign "		\
+		"-working-directory $WORKING_DIR "		\
+		"-c \"$CLANG_SOURCE\" -target bpf -O2 -o -"
 
 struct llvm_param llvm_param = {
 	.clang_path = "clang",
@@ -326,8 +327,8 @@ get_kbuild_opts(char **kbuild_dir, char **kbuild_include_opts)
 int llvm__compile_bpf(const char *path, void **p_obj_buf,
 		      size_t *p_obj_buf_sz)
 {
-	int err;
-	char clang_path[PATH_MAX];
+	int err, nr_cpus_avail;
+	char clang_path[PATH_MAX], nr_cpus_avail_str[64];
 	const char *clang_opt = llvm_param.clang_opt;
 	const char *template = llvm_param.clang_bpf_cmd_template;
 	char *kbuild_dir = NULL, *kbuild_include_opts = NULL;
@@ -354,6 +355,17 @@ int llvm__compile_bpf(const char *path, void **p_obj_buf,
 	 */
 	get_kbuild_opts(&kbuild_dir, &kbuild_include_opts);
 
+	nr_cpus_avail = sysconf(_SC_NPROCESSORS_CONF);
+	if (nr_cpus_avail <= 0) {
+		pr_err(
+"WARNING:\tunable to get available CPUs in this system: %s\n"
+"        \tUse 128 instead.\n", strerror(errno));
+		nr_cpus_avail = 128;
+	}
+	snprintf(nr_cpus_avail_str, sizeof(nr_cpus_avail_str), "%d",
+		 nr_cpus_avail);
+
+	force_set_env("NR_CPUS", nr_cpus_avail_str);
 	force_set_env("CLANG_EXEC", clang_path);
 	force_set_env("CLANG_OPTIONS", clang_opt);
 	force_set_env("KERNEL_INC_OPTIONS", kbuild_include_opts);
-- 
1.8.3.4