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procfs: optimize seq_pad() to speed up /proc/pid/maps 

seq_printf() is slow and it can be replaced by memset() in this case.

== test.py
  num = 0
  with open("/proc/1/maps") as f:
          while num < 10000 :
                  data = f.read()
                  f.seek(0, 0)
                  num = num + 1
==

== Before patch ==
  $  time python test.py
  real	0m0.986s
  user	0m0.279s
  sys	0m0.707s

== After patch ==
  $ time python test.py
  real	0m0.932s
  user	0m0.261s
  sys	0m0.669s

$ perf record -g python test.py
== Before patch ==
-   47.35%     3.38%  python   [kernel.kallsyms] [k] show_map_vma.isra.23
   - 43.97% show_map_vma.isra.23
      + 20.84% seq_path
      - 15.73% show_vma_header_prefix
      + 6.96% seq_pad
   + 2.94% __GI___libc_read

== After patch ==
-   44.01%     0.34%  python   [kernel.kallsyms] [k] show_pid_map
   - 43.67% show_pid_map
      - 42.91% show_map_vma.isra.23
         + 21.55% seq_path
         - 15.68% show_vma_header_prefix
         + 2.08% seq_pad
        0.55% seq_putc

Link: http://lkml.kernel.org/r/20180112185812.7710-2-avagin@openvz.org
Signed-off-by: Andrei Vagin <avagin@openvz.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrei Vagin 2018-04-10 16:30:47 -07:00 committed by Linus Torvalds
parent 0e3dc01914
commit 8cfa67b4d9
1 changed files with 8 additions and 2 deletions
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10
fs/seq_file.c
View File

@ -828,8 +828,14 @@ EXPORT_SYMBOL(seq_write);
void seq_pad(struct seq_file *m, char c)
{
int size = m->pad_until - m->count;
if (size > 0)
seq_printf(m, "%*s", size, "");
if (size > 0) {
if (size + m->count > m->size) {
seq_set_overflow(m);
return;
}
memset(m->buf + m->count, ' ', size);
m->count += size;
}
if (c)
seq_putc(m, c);
}