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SubjectRe: [PATCH] Add num_to_str() for speedup /proc/stat
On Mon, 30 Jan 2012 14:16:19 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Date: Mon, 30 Jan 2012 14:15:12 +0900
> Subject: [PATCH] Add num_to_str() for speedup /proc/stat
>
> At reading /proc/stat, most of time is consumed by vsnprintf() at el.
>
> Here is a test script, reading /proc/stat 1000 times..
>
> == stat_check.py
> num = 0
> with open("/proc/stat") as f:
> while num < 1000 :
> data = f.read()
> f.seek(0, 0)
> num = num + 1
> ==
>
> perf shows
>
> 20.39% stat_check.py [kernel.kallsyms] [k] format_decode
> 13.41% stat_check.py [kernel.kallsyms] [k] number
> 12.61% stat_check.py [kernel.kallsyms] [k] vsnprintf
> 10.85% stat_check.py [kernel.kallsyms] [k] memcpy
> 4.85% stat_check.py [kernel.kallsyms] [k] radix_tree_lookup
> 4.43% stat_check.py [kernel.kallsyms] [k] seq_printf
>
> This patch removes most of calls to vsnprintf() by adding
> num_to_str() and seq_print_decimal_ull(), which prints decimal numbers
> without rich functions provided by printf().
>
> On my 8cpu box.
> == Before patch ==
> [root@bluextal test]# time ./stat_check.py
>
> real 0m0.150s
> user 0m0.026s
> sys 0m0.121s
>
> == After patch ==
> [root@bluextal test]# time ./stat_check.py
>
> real 0m0.055s
> user 0m0.022s
> sys 0m0.030s
>
> Maybe it's worth to add this simple function.

I suppose so - the new infrastructure can be used elsewhere.

I tried doing the

if (kstst_irqs(j) == 0) {
seq_putc(p, ' ');
seq_putc(p, '0');
think on top of this and didn't observe any improvement.


I made some changes - please review. I'm not sure why you did "char
tmp[66]"?


From: Andrew Morton <akpm@linux-foundation.org>
Subject: procfs-add-num_to_str-to-speed-up-proc-stat-fix

- remove incorrect comment
- use less stack in num_to_str()
- move comment from .h to .c
- simplify seq_put_decimal_ull()

Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Paul Turner <pjt@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
fs/seq_file.c | 5 ++---
include/linux/kernel.h | 6 ------
include/linux/seq_file.h | 4 +---
lib/vsprintf.c | 8 +++++++-
4 files changed, 10 insertions(+), 13 deletions(-)
diff -puN fs/proc/stat.c~procfs-add-num_to_str-to-speed-up-proc-stat-fix fs/proc/stat.c
diff -puN fs/seq_file.c~procfs-add-num_to_str-to-speed-up-proc-stat-fix fs/seq_file.c
--- a/fs/seq_file.c~procfs-add-num_to_str-to-speed-up-proc-stat-fix
+++ a/fs/seq_file.c
@@ -659,14 +659,13 @@ int seq_put_decimal_ull(struct seq_file
if (m->count + 2 >= m->size) /* we'll write 2 bytes at least */
goto overflow;

+ m->buf[m->count++] = delimiter;
+
if (num < 10) {
- m->buf[m->count++] = delimiter;
m->buf[m->count++] = num + '0';
return 0;
}

- m->buf[m->count++] = delimiter;
-
len = num_to_str(m->buf + m->count, m->size - m->count, num);
if (!len)
goto overflow;
diff -puN include/linux/kernel.h~procfs-add-num_to_str-to-speed-up-proc-stat-fix include/linux/kernel.h
--- a/include/linux/kernel.h~procfs-add-num_to_str-to-speed-up-proc-stat-fix
+++ a/include/linux/kernel.h
@@ -299,12 +299,6 @@ extern long long simple_strtoll(const ch
#define strict_strtoull kstrtoull
#define strict_strtoll kstrtoll

-/*
- * Convert passed number to decimal string.
- * returns returns the length of string. at buffer overflow, returns 0.
- *
- * If speed is not important, use snprintf(). It's easy to read the code.
- */
extern int num_to_str(char *buf, int size, unsigned long long num);

/* lib/printf utilities */
diff -puN include/linux/seq_file.h~procfs-add-num_to_str-to-speed-up-proc-stat-fix include/linux/seq_file.h
--- a/include/linux/seq_file.h~procfs-add-num_to_str-to-speed-up-proc-stat-fix
+++ a/include/linux/seq_file.h
@@ -121,10 +121,8 @@ int single_release(struct inode *, struc
void *__seq_open_private(struct file *, const struct seq_operations *, int);
int seq_open_private(struct file *, const struct seq_operations *, int);
int seq_release_private(struct inode *, struct file *);
-
-/* defined in lib/vsprintf.c */
int seq_put_decimal_ull(struct seq_file *m, char delimiter,
- unsigned long long num);
+ unsigned long long num);

#define SEQ_START_TOKEN ((void *)1)
/*
diff -puN lib/vsprintf.c~procfs-add-num_to_str-to-speed-up-proc-stat-fix lib/vsprintf.c
--- a/lib/vsprintf.c~procfs-add-num_to_str-to-speed-up-proc-stat-fix
+++ a/lib/vsprintf.c
@@ -212,9 +212,15 @@ char *put_dec(char *buf, unsigned long l
}
}

+/*
+ * Convert passed number to decimal string.
+ * Returns the length of string. On buffer overflow, returns 0.
+ *
+ * If speed is not important, use snprintf(). It's easy to read the code.
+ */
int num_to_str(char *buf, int size, unsigned long long num)
{
- char tmp[66];
+ char tmp[21]; /* Enough for 2^64 in decimal */
int idx, len;

len = put_dec(tmp, num) - tmp;
_


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