linux-kernel - Re: [PATCH 1/4] perf tools: Pass available CPU number to clang compiler

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Date:	Wed, 4 Nov 2015 19:09:53 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Wang Nan <wangnan0@...wei.com>
Cc:	namhyung@...nel.org, lizefan@...wei.com, pi3orama@....com,
	linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>
Subject: Re: [PATCH 1/4] perf tools: Pass available CPU number to clang
 compiler

Em Wed, Nov 04, 2015 at 11:20:04AM +0000, Wang Nan escreveu:
> This patch introduces a new macro "__NR_CPUS__" to perf's embedded
> clang compiler, which represent the available CPU counters in this

available "CPU counters"? ENOPARSE :-)

> system. BPF program can use this macro to create a map with same
> number of system CPUs. For exmaple:
                             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__,
>  };

I wonder if we shouldn't use the getconf() parameter here, i.e. define
_SC_NPROCESSORS_CONF and also provide _SC_NPROCESSORS_ONLN.

The kernel uses NR_CPUS, for accessing CONFIG_NR_CPUS, Alexei, what do
you think?

- Arnaldo
 
> Signed-off-by: Wang Nan <wangnan0@...wei.com>
> Cc: Arnaldo Carvalho de Melo <acme@...hat.com>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Zefan Li <lizefan@...wei.com>
> Cc: pi3orama@....com
> ---
>  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
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