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

Browse source 
== 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

[[email protected]: remove incorrect comment, use less statck in num_to_str(), move comment from .h to .c, simplify seq_put_decimal_ull()]
[[email protected]: avoid breaking the ABI in /proc/stat]
Signed-off-by: KAMEZAWA Hiroyuki <[email protected]>
Signed-off-by: Andrea Righi <[email protected]>
Cc: Eric Dumazet <[email protected]>
Cc: Glauber Costa <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Paul Turner <[email protected]>
Cc: Russell King <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
KAMEZAWA Hiroyuki 2012-03-23 15:02:54 -07:00 • committed by Linus Torvalds
commit 1ac101a5d6
5 changed files with 84 additions and 29 deletions
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;