linux-kernel - [PATCH 08/13] proc: convert /proc/*/fd to _print

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Message-Id: <20180827231503.26899-8-adobriyan@gmail.com>
Date:   Tue, 28 Aug 2018 02:14:58 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org, Alexey Dobriyan <adobriyan@...il.com>
Subject: [PATCH 08/13] proc: convert /proc/*/fd to _print_integer()

Benchmark opendir+readdir("/proc/self/fd")+closedir 2^21 times
with 4 descriptors (0, 1, 2, 3 from opendir):

	11.802099126 seconds time elapsed ( +-  0.23% )
	10.950810068 seconds time elapsed ( +-  0.23% )

	-7.2%

Benchmark the same thing with 1000 descriptors:

	362.1250 us per iteration
	288.4375 us

	-20%

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---
 fs/proc/fd.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index e098302b5101..60ad1935eefc 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -247,8 +247,7 @@ static int proc_readfd_common(struct file *file, struct dir_context *ctx,
 	     fd++, ctx->pos++) {
 		struct file *f;
 		struct fd_data data;
-		char name[10 + 1];
-		unsigned int len;
+		char name[10], *p = name + sizeof(name);
 
 		f = fcheck_files(files, fd);
 		if (!f)
@@ -257,9 +256,10 @@ static int proc_readfd_common(struct file *file, struct dir_context *ctx,
 		rcu_read_unlock();
 		data.fd = fd;
 
-		len = snprintf(name, sizeof(name), "%u", fd);
+		p = _print_integer_u32(p, fd);
 		if (!proc_fill_cache(file, ctx,
-				     name, len, instantiate, tsk,
+				     p, name + sizeof(name) - p,
+				     instantiate, tsk,
 				     &data))
 			goto out_fd_loop;
 		cond_resched();
-- 
2.16.4