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procfs: add num_to_str() to speed up /proc/stat 

== 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

[akpm@linux-foundation.org: remove incorrect comment, use less statck in num_to_str(), move comment from .h to .c, simplify seq_put_decimal_ull()]
[andrea@betterlinux.com: avoid breaking the ABI in /proc/stat]
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrea Righi <andrea@betterlinux.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Glauber Costa <glommer@parallels.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Turner <pjt@google.com>
Cc: Russell King <rmk@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
KAMEZAWA Hiroyuki 2012-03-23 15:02:54 -07:00 committed by Linus Torvalds
parent 59a32e2ce5
commit 1ac101a5d6
5 changed files with 84 additions and 29 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

55
fs/proc/stat.c
View File

@ -89,18 +89,19 @@ static int show_stat(struct seq_file *p, void *v)
}
sum += arch_irq_stat();
seq_printf(p, "cpu %llu %llu %llu %llu %llu %llu %llu %llu %llu "
"%llu\n",
(unsigned long long)cputime64_to_clock_t(user),
(unsigned long long)cputime64_to_clock_t(nice),
(unsigned long long)cputime64_to_clock_t(system),
(unsigned long long)cputime64_to_clock_t(idle),
(unsigned long long)cputime64_to_clock_t(iowait),
(unsigned long long)cputime64_to_clock_t(irq),
(unsigned long long)cputime64_to_clock_t(softirq),
(unsigned long long)cputime64_to_clock_t(steal),
(unsigned long long)cputime64_to_clock_t(guest),
(unsigned long long)cputime64_to_clock_t(guest_nice));
seq_puts(p, "cpu ");
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(user));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(nice));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(system));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(idle));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(iowait));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(irq));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(softirq));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(steal));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest_nice));
seq_putc(p, '\n');
for_each_online_cpu(i) {
/* Copy values here to work around gcc-2.95.3, gcc-2.96 */
user = kcpustat_cpu(i).cpustat[CPUTIME_USER];
@ -113,26 +114,24 @@ static int show_stat(struct seq_file *p, void *v)
steal = kcpustat_cpu(i).cpustat[CPUTIME_STEAL];
guest = kcpustat_cpu(i).cpustat[CPUTIME_GUEST];
guest_nice = kcpustat_cpu(i).cpustat[CPUTIME_GUEST_NICE];
seq_printf(p,
"cpu%d %llu %llu %llu %llu %llu %llu %llu %llu %llu "
"%llu\n",
i,
(unsigned long long)cputime64_to_clock_t(user),
(unsigned long long)cputime64_to_clock_t(nice),
(unsigned long long)cputime64_to_clock_t(system),
(unsigned long long)cputime64_to_clock_t(idle),
(unsigned long long)cputime64_to_clock_t(iowait),
(unsigned long long)cputime64_to_clock_t(irq),
(unsigned long long)cputime64_to_clock_t(softirq),
(unsigned long long)cputime64_to_clock_t(steal),
(unsigned long long)cputime64_to_clock_t(guest),
(unsigned long long)cputime64_to_clock_t(guest_nice));
seq_printf(p, "cpu%d", i);
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(user));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(nice));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(system));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(idle));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(iowait));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(irq));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(softirq));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(steal));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest));
seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest_nice));
seq_putc(p, '\n');
}
seq_printf(p, "intr %llu", (unsigned long long)sum);
/* sum again ? it could be updated? */
for_each_irq_nr(j)
seq_printf(p, " %u", kstat_irqs(j));
seq_put_decimal_ull(p, ' ', kstat_irqs(j));
seq_printf(p,
"\nctxt %llu\n"
@ -149,7 +148,7 @@ static int show_stat(struct seq_file *p, void *v)
seq_printf(p, "softirq %llu", (unsigned long long)sum_softirq);
for (i = 0; i < NR_SOFTIRQS; i++)
seq_printf(p, " %u", per_softirq_sums[i]);
seq_put_decimal_ull(p, ' ', per_softirq_sums[i]);
seq_putc(p, '\n');
return 0;

33
fs/seq_file.c
View File

@ -644,6 +644,39 @@ int seq_puts(struct seq_file *m, const char *s)
}
EXPORT_SYMBOL(seq_puts);
/*
* A helper routine for putting decimal numbers without rich format of printf().
* only 'unsigned long long' is supported.
* This routine will put one byte delimiter + number into seq_file.
* This routine is very quick when you show lots of numbers.
* In usual cases, it will be better to use seq_printf(). It's easier to read.
*/
int seq_put_decimal_ull(struct seq_file *m, char delimiter,
unsigned long long num)
{
int len;
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++] = num + '0';
return 0;
}
len = num_to_str(m->buf + m->count, m->size - m->count, num);
if (!len)
goto overflow;
m->count += len;
return 0;
overflow:
m->count = m->size;
return -1;
}
EXPORT_SYMBOL(seq_put_decimal_ull);
/**
* seq_write - write arbitrary data to buffer
* @seq: seq_file identifying the buffer to which data should be written

2
include/linux/kernel.h
View File

@ -312,6 +312,8 @@ extern long long simple_strtoll(const char *,char **,unsigned int);
#define strict_strtoull kstrtoull
#define strict_strtoll kstrtoll
extern int num_to_str(char *buf, int size, unsigned long long num);
/* lib/printf utilities */
extern __printf(2, 3) int sprintf(char *buf, const char * fmt, ...);

3
include/linux/seq_file.h
View File

@ -121,9 +121,10 @@ int single_release(struct inode *, struct file *);
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 *);
int seq_put_decimal_ull(struct seq_file *m, char delimiter,
unsigned long long num);
#define SEQ_START_TOKEN ((void *)1)
/*
* Helpers for iteration over list_head-s in seq_files
*/

20
lib/vsprintf.c
View File

@ -212,6 +212,26 @@ char *put_dec(char *buf, unsigned long long num)
}
}
/*
* 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[21]; /* Enough for 2^64 in decimal */
int idx, len;
len = put_dec(tmp, num) - tmp;
if (len > size)
return 0;
for (idx = 0; idx < len; ++idx)
buf[idx] = tmp[len - idx - 1];
return len;
}
#define ZEROPAD 1 /* pad with zero */
#define SIGN 2 /* unsigned/signed long */
#define PLUS 4 /* show plus */