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authorKAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>2012-03-23 15:02:54 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2012-03-23 16:58:42 -0700
commit1ac101a5d675aca2426c5cd460c73fb95acb8391 (patch)
tree5d993fde0c5e67de97c0d9ffac54163f06fc90c9 /lib/vsprintf.c
parent59a32e2ce5eb809967cac4e718bc527beca83c59 (diff)
downloadlinux-1ac101a5d675aca2426c5cd460c73fb95acb8391.tar.gz
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>
Diffstat (limited to 'lib/vsprintf.c')
-rw-r--r--lib/vsprintf.c20
1 files changed, 20 insertions, 0 deletions
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 38e612e66da..385c40291cd 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -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 */