procfs: speed up /proc/pid/stat, statm
Process accounting applications as top, ps visit some files under
/proc/<pid>. With seq_put_decimal_ull(), we can optimize /proc/<pid>/stat
and /proc/<pid>/statm files.
This patch adds
- seq_put_decimal_ll() for signed values.
- allow delimiter == 0.
- convert seq_printf() to seq_put_decimal_ull/ll in /proc/stat, statm.
Test result on a system with 2000+ procs.
Before patch:
[kamezawa@bluextal test]$ top -b -n 1 | wc -l
2223
[kamezawa@bluextal test]$ time top -b -n 1 > /dev/null
real 0m0.675s
user 0m0.044s
sys 0m0.121s
[kamezawa@bluextal test]$ time ps -elf > /dev/null
real 0m0.236s
user 0m0.056s
sys 0m0.176s
After patch:
kamezawa@bluextal ~]$ time top -b -n 1 > /dev/null
real 0m0.657s
user 0m0.052s
sys 0m0.100s
[kamezawa@bluextal ~]$ time ps -elf > /dev/null
real 0m0.198s
user 0m0.050s
sys 0m0.145s
Considering top, ps tend to scan /proc periodically, this will reduce cpu
consumption by top/ps to some extent.
[akpm@linux-foundation.org: checkpatch fixes]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 7d19816..55c293f 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -659,7 +659,8 @@
if (m->count + 2 >= m->size) /* we'll write 2 bytes at least */
goto overflow;
- m->buf[m->count++] = delimiter;
+ if (delimiter)
+ m->buf[m->count++] = delimiter;
if (num < 10) {
m->buf[m->count++] = num + '0';
@@ -677,6 +678,24 @@
}
EXPORT_SYMBOL(seq_put_decimal_ull);
+int seq_put_decimal_ll(struct seq_file *m, char delimiter,
+ long long num)
+{
+ if (num < 0) {
+ if (m->count + 3 >= m->size) {
+ m->count = m->size;
+ return -1;
+ }
+ if (delimiter)
+ m->buf[m->count++] = delimiter;
+ num = -num;
+ delimiter = '-';
+ }
+ return seq_put_decimal_ull(m, delimiter, num);
+
+}
+EXPORT_SYMBOL(seq_put_decimal_ll);
+
/**
* seq_write - write arbitrary data to buffer
* @seq: seq_file identifying the buffer to which data should be written