From 209b14dc030760d3a17029a5c3bd92c9d6fd3f37 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Mon, 12 Dec 2016 16:45:25 -0800 Subject: [PATCH] fs/proc/array.c: slightly improve render_sigset_t 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 Acked-by: Andrei Vagin Acked-by: Kees Cook Cc: Alexey Dobriyan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/array.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/proc/array.c b/fs/proc/array.c index 082676ab4878..51a4213afa2e 100644 --- a/fs/proc/array.c +++ b/fs/proc/array.c @@ -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+3)) x |= 4; if (sigismember(set, i+4)) x |= 8; - seq_printf(m, "%x", x); + seq_putc(m, hex_asc[x]); } while (i >= 4); seq_putc(m, '\n'); -- 2.39.5