Commit 1ac101a5 authored by KAMEZAWA Hiroyuki's avatar KAMEZAWA Hiroyuki Committed by Linus Torvalds
Browse files

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: default avatarKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: default avatarAndrea 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 59a32e2c

fs/proc/stat.c

+27 −28
Original line number Diff line number Diff line
@@ -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;

fs/seq_file.c

+33 −0
Original line number Diff line number Diff line
@@ -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

include/linux/kernel.h

+2 −0
Original line number Diff line number Diff line
@@ -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, ...);

include/linux/seq_file.h

+2 −1
Original line number Diff line number Diff line
@@ -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

 */

lib/vsprintf.c

+20 −0
Original line number Diff line number Diff line
@@ -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 */

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