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proc: speed up /proc/stat handling 

On a typical 16 cpus machine, "cat /proc/stat" gives more than 4096 bytes,
and is slow :

  # strace -T -o /tmp/STRACE cat /proc/stat | wc -c
  5826
  # grep "cpu " /tmp/STRACE
  read(0, "cpu  1949310 19 2144714 12117253"..., 32768) = 5826 <0.001504>

Thats partly because show_stat() must be called twice since initial
buffer size is too small (4096 bytes for less than 32 possible cpus)

Fix this by :

 1) Taking into account nr_irqs in the initial buffer sizing.

 2) Using ksize() to allow better filling of initial buffer.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eric Dumazet 2012-03-23 15:02:53 -07:00 committed by Linus Torvalds
parent b908243c54
commit 59a32e2ce5
1 changed files with 5 additions and 2 deletions
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7
fs/proc/stat.c
View File

@ -157,11 +157,14 @@ static int show_stat(struct seq_file *p, void *v)
static int stat_open(struct inode *inode, struct file *file)
{
unsigned size = 4096 * (1 + num_possible_cpus() / 32);
unsigned size = 1024 + 128 * num_possible_cpus();
char *buf;
struct seq_file *m;
int res;
/* minimum size to display an interrupt count : 2 bytes */
size += 2 * nr_irqs;
/* don't ask for more than the kmalloc() max size */
if (size > KMALLOC_MAX_SIZE)
size = KMALLOC_MAX_SIZE;
@ -173,7 +176,7 @@ static int stat_open(struct inode *inode, struct file *file)
if (!res) {
m = file->private_data;
m->buf = buf;
m->size = size;
m->size = ksize(buf);
} else
kfree(buf);
return res;