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Date: Wed, 9 Nov 2016 13:40:47 -0800 From: Andrei Vagin <avagin@...il.com> To: Rasmus Villemoes <linux@...musvillemoes.dk> Cc: Andrew Morton <akpm@...ux-foundation.org>, Kees Cook <keescook@...omium.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] fs/proc/array.c: slightly improve render_sigset_t On Tue, Sep 20, 2016 at 3:28 PM, Rasmus Villemoes <linux@...musvillemoes.dk> wrote: > 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); > } > Acked-by: Andrei Vagin <avagin@...nvz.org> Andrew, could you replace my patch "proc-optimize-render_sigset_t.patch" to this one. Thanks, Andrei > Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.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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