[PATCH] proc: optimize render_sigset_t()

[PATCH] proc: optimize render_sigset_t()

[Andrei Vagin]

render_sigset_t() requires about 30% of time to generate
/proc/pid/status.

- 74.44% sys_read
 - 74.40% vfs_read
    - 74.01% __vfs_read
       - 73.36% seq_read
          - 72.97% proc_single_show
             - 72.26% proc_pid_status
                + 29.79% render_sigset_t
                + 11.47% task_mem
                + 5.60% render_cap_t
                + 4.95% seq_printf
                + 4.28% cpuset_task_status_allowed

seq_printf is called for each symbol of a signal mask. This patch
collect a whole mask in a buffer and prints it for one call of
seq_puts().

  - 65.02% proc_single_show
     - 63.75% proc_pid_status
        + 15.73% task_mem
        + 7.42% render_sigset_t
        + 7.39% render_cap_t
        + 6.46% cpuset_task_status_allowed

/proc/pid/status is generated 25% faster with this optimization.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrei Vagin <avagin@openvz.org>
---
 fs/proc/array.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 81818ad..0190c3e 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -232,11 +232,13 @@ static inline void task_state(struct seq_file *m, struct pid_namespace *ns,
 void render_sigset_t(struct seq_file *m, const char *header,
 				sigset_t *set)
 {
-	int i;
+	char buf[_NSIG / 4 + 2];
+	int i, j;
 
 	seq_puts(m, header);
 
 	i = _NSIG;
+	j = 0;
 	do {
 		int x = 0;
 
@@ -245,10 +247,13 @@ void render_sigset_t(struct seq_file *m, const char *header,
 		if (sigismember(set, i+2)) x |= 2;
 		if (sigismember(set, i+3)) x |= 4;
 		if (sigismember(set, i+4)) x |= 8;
-		seq_printf(m, "%x", x);
+		buf[j++] = hex_asc[x];
 	} while (i >= 4);
 
-	seq_putc(m, '\n');
+	buf[j++] = '\n';
+	buf[j++] = 0;
+
+	seq_puts(m, buf);
 }
 
 static void collect_sigign_sigcatch(struct task_struct *p, sigset_t *ign,
-- 
2.7.4

Re: [PATCH] proc: optimize render_sigset_t()

[Alexey Dobriyan]

On Wed, Nov 9, 2016 at 12:37 AM, Andrei Vagin <avagin@openvz.org> wrote:

> @@ -245,10 +247,13 @@ void render_sigset_t(struct seq_file *m, const char *header,
>                 if (sigismember(set, i+2)) x |= 2;
>                 if (sigismember(set, i+3)) x |= 4;
>                 if (sigismember(set, i+4)) x |= 8;
> -               seq_printf(m, "%x", x);
> +               buf[j++] = hex_asc[x];
>         } while (i >= 4);
>
> -       seq_putc(m, '\n');
> +       buf[j++] = '\n';
> +       buf[j++] = 0;
> +
> +       seq_puts(m, buf);

seq_write() should be used to avoid re-reading in strlen().
Anyway I suspect bulk conversion SIMD-style will still be faster.


     Alexey