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fs/proc/array.c: slightly improve render_sigset_t

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format_decode and vsnprintf occasionally show up in perf top, so I went
looking for places that might not need the full printf power.  With the
help of kprobes, I gathered some statistics on which format strings we
mostly pass to vsnprintf.  On a trivial desktop workload, I hit "%x" 25%
of the time, so something apparently reads /proc/pid/status (which does
5*16 printf("%x") calls) a lot.

With this patch, reading /proc/pid/status is 30% faster according to
this microbenchmark:

	char buf[4096];
	int i, fd;
	for (i = 0; i < 10000; ++i) {
		fd = open("/proc/self/status", O_RDONLY);
		read(fd, buf, sizeof(buf));
		close(fd);
	}

Link: http://lkml.kernel.org/r/1474410485-1305-1-git-send-email-linux@rasmusvillemoes.dk
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Acked-by: Andrei Vagin <avagin@openvz.org>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Rasmus Villemoes 2016-12-12 16:45:25 -08:00 committed by Linus Torvalds
parent 492b2da605
commit 209b14dc03
1 changed files with 1 additions and 1 deletions
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fs/proc/array.c
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@ -245,7 +245,7 @@ void render_sigset_t(struct seq_file *m, const char *header,
if (sigismember(set, i+2)) x |= 2; if (sigismember(set, i+2)) x |= 2;
if (sigismember(set, i+3)) x |= 4; if (sigismember(set, i+3)) x |= 4;
if (sigismember(set, i+4)) x |= 8; if (sigismember(set, i+4)) x |= 8;
seq_printf(m, "%x", x); seq_putc(m, hex_asc[x]);
} while (i >= 4); } while (i >= 4);
seq_putc(m, '\n'); seq_putc(m, '\n');