[igt-dev] [PATCH i-g-t] intel-gpu-top: Optimise the scanning loop a bit

[Tvrtko Ursulin]

+ Umesh

If you have time this is an easy improvement extracted from the "vendor 
agnostic gputop" series.

Regards,

Tvrtko

On 06/06/2022 14:27, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Opendir(3) and fdopendir(3) are quite expensive system calls when ran in
> a loop which iterates all processes in a system times all open files in
> each.
> 
> Replace some of them (easy ones) with simpler open(2)/read(2) combo to
> avoid hammering on the malloc/free.
> 
> This brings the default CPU usage of the tool on my desktop from ~3% to
> ~2%.
> 
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>   tools/intel_gpu_top.c | 66 +++++++++++++++++++------------------------
>   1 file changed, 29 insertions(+), 37 deletions(-)
> 
> diff --git a/tools/intel_gpu_top.c b/tools/intel_gpu_top.c
> index 997aff582ff7..6de8a164fcff 100644
> --- a/tools/intel_gpu_top.c
> +++ b/tools/intel_gpu_top.c
> @@ -1022,12 +1022,12 @@ static void free_clients(struct clients *clients)
>   	free(clients);
>   }
>   
> -static bool is_drm_fd(DIR *fd_dir, const char *name)
> +static bool is_drm_fd(int fd_dir, const char *name)
>   {
>   	struct stat stat;
>   	int ret;
>   
> -	ret = fstatat(dirfd(fd_dir), name, &stat, 0);
> +	ret = fstatat(fd_dir, name, &stat, 0);
>   
>   	return ret == 0 &&
>   	       (stat.st_mode & S_IFMT) == S_IFCHR &&
> @@ -1054,12 +1054,12 @@ static bool get_task_name(const char *buffer, char *out, unsigned long sz)
>   	return true;
>   }
>   
> -static DIR *opendirat(DIR *at, const char *name)
> +static DIR *opendirat(int at, const char *name)
>   {
>   	DIR *dir;
>   	int fd;
>   
> -	fd = openat(dirfd(at), name, O_DIRECTORY);
> +	fd = openat(at, name, O_DIRECTORY);
>   	if (fd < 0)
>   		return NULL;
>   
> @@ -1070,37 +1070,27 @@ static DIR *opendirat(DIR *at, const char *name)
>   	return dir;
>   }
>   
> -static FILE *fropenat(DIR *at, const char *name)
> +static size_t readat2buf(int at, const char *name, char *buf, const size_t sz)
>   {
> -	FILE *f;
> +	ssize_t count;
>   	int fd;
>   
> -	fd = openat(dirfd(at), name, O_RDONLY);
> -	if (fd < 0)
> -		return NULL;
> +	fd = openat(at, name, O_RDONLY);
> +	if (fd <= 0)
> +		return 0;
>   
> -	f = fdopen(fd, "r");
> -	if (!f)
> -		close(fd);
> +	count = read(fd, buf, sz - 1);
> +	close(fd);
>   
> -	return f;
> -}
> +	if (count > 0) {
> +		buf[count] = 0;
>   
> -static size_t freadat2buf(char *buf, const size_t sz, DIR *at, const char *name)
> -{
> -	size_t count;
> -	FILE *f;
> +		return count;
> +	} else {
> +		buf[0] = 0;
>   
> -	f = fropenat(at, name);
> -	if (!f)
>   		return 0;
> -
> -	buf[sz - 1] = 0;
> -	count = fread(buf, 1, sz, f);
> -	buf[count - 1] = 0;
> -	fclose(f);
> -
> -	return count;
> +	}
>   }
>   
>   static struct clients *scan_clients(struct clients *clients, bool display)
> @@ -1126,10 +1116,11 @@ static struct clients *scan_clients(struct clients *clients, bool display)
>   		return clients;
>   
>   	while ((proc_dent = readdir(proc_dir)) != NULL) {
> -		DIR *pid_dir = NULL, *fd_dir = NULL, *fdinfo_dir = NULL;
> +		int pid_dir = -1, fd_dir = -1;
>   		struct dirent *fdinfo_dent;
>   		char client_name[64] = { };
>   		unsigned int client_pid;
> +		DIR *fdinfo_dir = NULL;
>   		char buf[4096];
>   		size_t count;
>   
> @@ -1138,11 +1129,12 @@ static struct clients *scan_clients(struct clients *clients, bool display)
>   		if (!isdigit(proc_dent->d_name[0]))
>   			continue;
>   
> -		pid_dir = opendirat(proc_dir, proc_dent->d_name);
> -		if (!pid_dir)
> +		pid_dir = openat(dirfd(proc_dir), proc_dent->d_name,
> +				 O_DIRECTORY | O_RDONLY);
> +		if (pid_dir < 0)
>   			continue;
>   
> -		count = freadat2buf(buf, sizeof(buf), pid_dir, "stat");
> +		count = readat2buf(pid_dir, "stat", buf, sizeof(buf));
>   		if (!count)
>   			goto next;
>   
> @@ -1153,8 +1145,8 @@ static struct clients *scan_clients(struct clients *clients, bool display)
>   		if (!get_task_name(buf, client_name, sizeof(client_name)))
>   			goto next;
>   
> -		fd_dir = opendirat(pid_dir, "fd");
> -		if (!fd_dir)
> +		fd_dir = openat(pid_dir, "fd", O_DIRECTORY | O_RDONLY);
> +		if (fd_dir < 0)
>   			goto next;
>   
>   		fdinfo_dir = opendirat(pid_dir, "fdinfo");
> @@ -1196,10 +1188,10 @@ static struct clients *scan_clients(struct clients *clients, bool display)
>   next:
>   		if (fdinfo_dir)
>   			closedir(fdinfo_dir);
> -		if (fd_dir)
> -			closedir(fd_dir);
> -		if (pid_dir)
> -			closedir(pid_dir);
> +		if (fd_dir >= 0)
> +			close(fd_dir);
> +		if (pid_dir >= 0)
> +			close(pid_dir);
>   	}
>   
>   	closedir(proc_dir);