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

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