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);
}
Signed-off-by: Rasmus Villemoes <li...@rasmusvillemoes.dk>
---
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 88c7de12197b..7f73b689a15c 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -251,7 +251,7 @@ 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');
--
2.1.4
