linux-kernel - [PATCH] printk: trivial optimizations

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Message-Id: <200711081457.32211.vda.linux@googlemail.com>
Date:	Thu, 8 Nov 2007 14:57:32 -0700
From:	Denys Vlasenko <vda.linux@...glemail.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] printk: trivial optimizations

Hi Andrew,

This patch exploits some optimization opportunities
similar to those in first two patches I sent a while ago.

In particular:

In arch/x86/boot/printf.c gets rid of unused tail of digits:
const char *digits = "0123456789abcdefghijklmnopqrstuvwxyz";
(we are using 0-9a-f only)

Uses smaller/faster lowercasing (by ORing with 0x20)
if we know that we work on numbers/digits. Makes
strtoul smaller, and also we are getting rid of 
  static const char small_digits[] = "0123456789abcdefx";
  static const char large_digits[] = "0123456789ABCDEFX";
since this works equally well:
  static const char digits[16] = "0123456789ABCDEF";

Size savings:

$ size vmlinux.org vmlinux
   text    data     bss     dec     hex filename
 877320  112252   90112 1079684  107984 vmlinux.org
 877048  112252   90112 1079412  107874 vmlinux

It may be also a tiny bit faster because code has less
branches now, but I doubt it is measurable.

Patch is run-tested.

Signed-off-by: Denys Vlasenko <vda.linux@...glemail.com>
-- 
vda

View attachment "linux-2.6.24-rc2-printf.patch" of type "text/x-diff" (6152 bytes)