[PATCH 3/4] linux: Use /sys/devices/system/cpu/possible on __get_nprocs_conf

[Adhemerval Zanella]

Ping.

On 29/03/2021 15:25, Adhemerval Zanella wrote:
> Instead of iterate over all the cpu in the sysfs folder.  It consumes
> slight less resources on large system (which might require extra
> getdents call) and memory (a limited stack buffer instead a large
> malloced one for opendir).
> 
> Checked on x86_64-linux-gnu, aarch64-linux-gnu, and
> powerpc64le-linux-gnu.
> ---
>  sysdeps/unix/sysv/linux/getsysstats.c | 51 +++++++++++++++------------
>  1 file changed, 29 insertions(+), 22 deletions(-)
> 
> diff --git a/sysdeps/unix/sysv/linux/getsysstats.c b/sysdeps/unix/sysv/linux/getsysstats.c
> index f8a4a31d1b..5069951246 100644
> --- a/sysdeps/unix/sysv/linux/getsysstats.c
> +++ b/sysdeps/unix/sysv/linux/getsysstats.c
> @@ -17,7 +17,8 @@
>     License along with the GNU C Library; if not, see
>     <https://www.gnu.org/licenses/>.  */
>  
> -#include <dirent.h>
> +#include <ctype.h>
> +#include <intprops.h>
>  #include <not-cancel.h>
>  #include <scratch_buffer.h>
>  #include <stdio.h>
> @@ -63,33 +64,39 @@ weak_alias (__get_nprocs, get_nprocs)
>  int
>  __get_nprocs_conf (void)
>  {
> -  /* XXX Here will come a test for the new system call.  */
> +  int result = 1;
>  
>    /* Try to use the sysfs filesystem.  It has actual information about
>       online processors.  */
> -  DIR *dir = __opendir ("/sys/devices/system/cpu");
> -  if (dir != NULL)
> +  int fd = __open64_nocancel ("/sys/devices/system/cpu/possible", O_RDONLY);
> +  if (fd != -1)
>      {
> -      int count = 0;
> -      struct dirent64 *d;
> -
> -      while ((d = __readdir64 (dir)) != NULL)
> -	/* NB: the sysfs has d_type support.  */
> -	if (d->d_type == DT_DIR && strncmp (d->d_name, "cpu", 3) == 0)
> -	  {
> -	    char *endp;
> -	    unsigned long int nr = strtoul (d->d_name + 3, &endp, 10);
> -	    if (nr != ULONG_MAX && endp != d->d_name + 3 && *endp == '\0')
> -	      ++count;
> -	  }
> -
> -      __closedir (dir);
> -
> -      return count;
> +      /* The entry is in the form of '[cpuX]-[cpuY]'.  */
> +      char buf[2 * INT_STRLEN_BOUND (unsigned int) + 1];
> +
> +      ssize_t n = __read_nocancel (fd, buf, sizeof (buf));
> +      if (n > 0)
> +	{
> +	  buf[n] = '\0';
> +
> +	  /* Start on the right, to find highest node number.  */
> +	  int m = 1;
> +	  while (--n)
> +	    {
> +	      if ((buf[n] == ',') || (buf[n] == '-'))
> +		break;
> +	      /* Ignore '\n'  */
> +	      if (! isdigit (buf[n]))
> +		continue;
> +	      result += (buf[n] - '0') * m;
> +	      m *= 10;
> +	    }
> +	}
> +
> +      __close_nocancel (fd);
> +      return result + 1;
>      }
>  
> -  int result = 1;
> -
>  #ifdef GET_NPROCS_CONF_PARSER
>    /* If we haven't found an appropriate entry return 1.  */
>    FILE *fp = fopen ("/proc/cpuinfo", "rce");
>