From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 10774C43381 for ; Sun, 24 Mar 2019 03:32:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BD81B2171F for ; Sun, 24 Mar 2019 03:32:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="KIszMrem" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728012AbfCXDb7 (ORCPT ); Sat, 23 Mar 2019 23:31:59 -0400 Received: from mail-ed1-f67.google.com ([209.85.208.67]:33260 "EHLO mail-ed1-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727808AbfCXDb6 (ORCPT ); Sat, 23 Mar 2019 23:31:58 -0400 Received: by mail-ed1-f67.google.com with SMTP id q3so4781972edg.0 for ; Sat, 23 Mar 2019 20:31:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=AqWwPpOhsA2o26o2fmZIc6acNEKi6Y6NFEG4S68lPUs=; b=KIszMremumzSDdJ3xuPEGgEipEtkj5zt6+55g2FJIl2mwoAqyD0quhSBjPAXzlMaJS hX1N5PRsNxPeqPQZ8sMOjEEkTVgXxvk+KOpAawLWerSoFL8/z67AP1aJndttHKaykzEx B+Cn6IRvyxl2GD5uyBciK0KzNyOjjqHNiQR7Ww5z+E3zWS4YTfF7AziChKCJC7FetjQj XhrCxTJyFk87PXXrI1Fj4mpw4zGmlxziTQg8/hKu6ZfsOkmB9ePDmxGFNw1kIrAPWGLH leua/G9u8yWmGmDvmpEEWrPYDLJjQf2cJXvtLAYgUcmaFlB+D1TTDGqLzpjvqwjuzIyp iWEw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=AqWwPpOhsA2o26o2fmZIc6acNEKi6Y6NFEG4S68lPUs=; b=mqRvAvCVNonyegJQ/aCZy9myT0paHvIhQ26SgSG3PpCzcL0rH2dReGMWu8KjBtSF3L bBRMj59NEITlXWvJM8FYQQAngjZ/LgvVpiYr8AHhtBwzof7SErerrRrauRhwIsS1qWI6 tYwBUHI1AtyH+2UyeLEbj0RSP1IfgJlTrhCUVhsqLWE4s8DPdskVV9VYXs6Focd0nKXC ZKNl6amZom7Ry0QjlH7H5kkgv5b7ArMycI9r3zsBjZ1j15R9XpYS+Pz3ixF3ePGNyjIR Si2geBszghDWog0h6u1cDJXMAPuWmxS34ZhJMet7ybTCajIB4E/X5FoZlCLqOIW8fJTZ qwZw== X-Gm-Message-State: APjAAAUEudd4RVeVqFvs0ENSa7G4LEAi0PFO/vi5dCPuYxKpyCW74Q3C dyLxDSzHFN0y4WkiSESUjBU= X-Google-Smtp-Source: APXvYqw5/MMKSmr+0EO5r5Lpx64jOIzYSkiixFWRORRjiKJsnpDQ60OlL/Sam/GH6eulbPVQJvsiAA== X-Received: by 2002:a17:906:924e:: with SMTP id c14mr9851030ejx.230.1553398316876; Sat, 23 Mar 2019 20:31:56 -0700 (PDT) Received: from archlinux-ryzen ([2a01:4f9:2a:1fae::2]) by smtp.gmail.com with ESMTPSA id d61sm4025148edd.96.2019.03.23.20.31.55 (version=TLS1_3 cipher=AEAD-AES256-GCM-SHA384 bits=256/256); Sat, 23 Mar 2019 20:31:55 -0700 (PDT) Date: Sat, 23 Mar 2019 20:31:53 -0700 From: Nathan Chancellor To: Sultan Alsawaf Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org, arnd@arndb.de, keescook@chromium.org, linux@rasmusvillemoes.dk, rostedt@goodmis.org, torvalds@linux-foundation.org, viro@zeniv.linux.org.uk Subject: Re: [RFCv2] string: Use faster alternatives when constant arguments are used Message-ID: <20190324033153.GA15815@archlinux-ryzen> References: <20190324014445.28688-1-sultan@kerneltoast.com> <20190324022406.GA18988@sultan-box.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190324022406.GA18988@sultan-box.localdomain> User-Agent: Mutt/1.11.4 (2019-03-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 23, 2019 at 07:24:06PM -0700, Sultan Alsawaf wrote: > I messed up the return value for strcat in the first patch. Here's a fixed > version, ready for some scathing reviews. > > From: Sultan Alsawaf > > When strcpy, strcat, and strcmp are used with a literal string, they can > be optimized to memcpy or memcmp calls. These alternatives are faster > since knowing the length of a string argument beforehand allows > traversal through the string word at a time without being concerned > about looking for the terminating zero character. In some cases, the > replaced calls to memcpy or memcmp can even be optimized out completely > for a significant speed up. > > Signed-off-by: Sultan Alsawaf > --- > include/linux/string.h | 30 ++++++++++++++++++++++++++++++ > 1 file changed, 30 insertions(+) > > diff --git a/include/linux/string.h b/include/linux/string.h > index 7927b875f..59c301c0e 100644 > --- a/include/linux/string.h > +++ b/include/linux/string.h > @@ -476,4 +476,34 @@ static __always_inline size_t str_has_prefix(const char *str, const char *prefix > return strncmp(str, prefix, len) == 0 ? len : 0; > } > > +/* > + * Replace some common string helpers with faster alternatives when one of the > + * arguments is a constant (i.e., literal string). This uses strlen instead of > + * sizeof for calculating the string length in order to silence compiler > + * warnings that may arise due to what the compiler thinks is incorrect sizeof > + * usage. The strlen calls on constants are folded into scalar values at compile > + * time, so performance is not reduced by using strlen. > + */ > +#define strcpy(dest, src) \ > + __builtin_choose_expr(__builtin_constant_p(src), \ > + memcpy((dest), (src), strlen(src) + 1), \ > + (strcpy)((dest), (src))) > + > +#define strcat(dest, src) \ > + __builtin_choose_expr(__builtin_constant_p(src), \ > + ({ \ > + memcpy(strchr((dest), '\0'), (src), strlen(src) + 1); \ > + (dest); \ > + }), \ > + (strcat)((dest), (src))) > + > +#define strcmp(dest, src) \ > + __builtin_choose_expr(__builtin_constant_p(dest), \ > + __builtin_choose_expr(__builtin_constant_p(src), \ > + (strcmp)((dest), (src)), \ > + memcmp((dest), (src), strlen(dest) + 1)), \ > + __builtin_choose_expr(__builtin_constant_p(src), \ > + memcmp((dest), (src), strlen(src) + 1), \ > + (strcmp)((dest), (src)))) > + > #endif /* _LINUX_STRING_H_ */ > -- > 2.21.0 > Explicitly cc'ing some folks who have touched include/linux/string.h in the past and might want to take a look at this. Nathan