perf llvm: Pass number of configured CPUs to clang compiler

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

 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: Alexei Starovoitov <ast@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/1446636007-239722-2-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

diff --git a/tools/perf/util/llvm-utils.c b/tools/perf/util/llvm-utils.c
index 4f6a478..80eecef 100644 (file)
--- 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);