From nobody Fri Dec 19 16:00:21 2025 Received: from mail-pl1-f176.google.com (mail-pl1-f176.google.com [209.85.214.176]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 80ACC2114 for ; Tue, 18 Mar 2025 03:43:15 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.176 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742269397; cv=none; b=BYkWyuM+LpjJieJPYKZG0rom+LdE8Vb3RQqrefpEvXtkxsMkAVlrsKV6k0BZuak/Xsv0hke+LJ5SAFemaaqim15bC+CKA78MkpYJXw2DqLLziNa1K11gDzeG+z1JUGX7u639F/EgFnrRcSR+t7cS5xYyNB9c+pL4Vmpmt7uh4Tg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1742269397; c=relaxed/simple; bh=zC4lcP2V4IiIPxr9JpgDGjzM2a58MVUtBq6gOOCS1H0=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=hGFdhwsaDq6ckYMk8ukpDUz+gaCRRN4GTJUVzZ8vGogxwaukatXWEZA6K+1R7tX6rOg5D1xW0SaPjhjhEc/vKTU3Z5ziamyMqQDUu8yNJHGvnCEEjBKchWBP5RtrVmQsDmMLJ6cfHLKQtvQuO5wb7mJbZGZ7tBY1AyakJSJrlN4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=aJfilUFh; arc=none smtp.client-ip=209.85.214.176 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="aJfilUFh" Received: by mail-pl1-f176.google.com with SMTP id d9443c01a7336-225df540edcso67953715ad.0 for ; Mon, 17 Mar 2025 20:43:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1742269394; x=1742874194; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:from:to:cc:subject:date:message-id:reply-to; bh=bbe7RI1DhdJmmq13I+ma0flbSEXGJRuSSXWMj76ljDs=; b=aJfilUFhClfaSBr7ZEFukmpuIgeFYtvompvDDhxEbskCGQvUifgYHTBtjDGvnzpoCx 5VR1VecFHPt8uTA8+170+mCnbgHMatwxDuTVKOVgnNJweC/U5FfOnBSCJgotu1g0oEmp mYB9x5v3IGox9bYUuQWwpVVgg8R5rtXfdk5OBlbLfNFQmcv+alED00m/pXYFeJslTaMv KIgrkofObAfXZOWB1RO5Nyekpi8KBEHyQFDzjKqXWpRtsAy+knEURt88+gaHGUnVh7Uc 6Ne9qByVinmZublq7ttK37IGZH4qUyBb5vtVUsUojnEod9Sc9D57yx9d+jTiQetBEgKM FrbA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1742269394; x=1742874194; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=bbe7RI1DhdJmmq13I+ma0flbSEXGJRuSSXWMj76ljDs=; b=anu7XTkyvsMb2iNaPP9F+hGi6BiynkaR7crYxPMJwTojzr35shqV96UkhUwptGaSIc +eGTu2n+FW6njTjepOB4sXikEI+Ec5b1NwvErp9fo7K4IZikELLYCsecbYLWmQrKZ/TT 3BTXZZpG12yRgJkIRrZ3mQ3wiEOjBDj+551xBybrfHcwRG3i/SEvdxUZoQGvaC9yqen1 /vvmjBTLXlcEaE5rQ1Bln1cd9Dm0pvNG/IVl6IoG7V27KbaB3qJW/BBPQhgXLoZykIDw 76327MKbKUMN6tgtPbYtUwH5vwt8fp3uvqSs4K0t1zMw0T0bmy/P90RFASMfskOZnq5P 976A== X-Gm-Message-State: AOJu0YyVu6l+HEtRZx6FzpkAvb5/E2Wj3yqs6b4/KpkDjsHfqWTjlycs 7iwxwqSItruKH2zN62gM9OuLc9M4emCr4M0w8eHR8cPm/Q6CEWHm X-Gm-Gg: ASbGncvN5sWV/so5j2SkZtKmKYVqh5h9vRGjUv8CNqSna/c1UVXzwqWcWGd7bJICBqU qqEFX4GUJ3ws2zmh0wlJQOHgZoyUyH2ZUCIKxaPatRh3TNCeIRDZ7GsnegSEbQ6+UQ3G9x5V/My Qskiviryrp+2LckKD7V4f9nmh2JwDbE9apy8YHFjPT95NkY4Y/NdKf0ZGMygpPoD3M1t04by1fz 8wseKmyCjR+HjjdyU5W3daUs+n90jW9maPdN/Z01Hpi9FO19F1gVebe2nEgoq69p1Q8AxKNSpzX 7yJsS6YT4B7syfqipsi3wHcDDkKLUGbtT2uLRGjT3trdcIWxgIZTccKAKO0m3g0B6B1st3L8 X-Google-Smtp-Source: AGHT+IFJQn/cOgw7EyLdb6WHd/Ewe8xwoPRaksNngkE4NI4fE8kg9IuFUAmiQpsXkIZKRDFRr5FG5g== X-Received: by 2002:a05:6a00:928c:b0:728:f21b:ce4c with SMTP id d2e1a72fcca58-73757794828mr2545778b3a.5.1742269394341; Mon, 17 Mar 2025 20:43:14 -0700 (PDT) Received: from vaxr-ASUSPRO-D840MB-M840MB.. ([2001:288:7001:2703:86b4:46:3f1e:43bf]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-737113d71fbsm8407612b3a.0.2025.03.17.20.43.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Mar 2025 20:43:13 -0700 (PDT) From: I Hsin Cheng To: hirofumi@mail.parknet.co.jp Cc: linux-kernel@vger.kernel.org, skhan@linuxfoundation.org, linux-kernel-mentees@lists.linux.dev, jserv@ccns.ncku.edu.tw, I Hsin Cheng Subject: [PATCH] fat: Refactor fat_tolower with branchless implementation Date: Tue, 18 Mar 2025 11:43:09 +0800 Message-ID: <20250318034309.920866-1-richard120310@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Elimate the need of if-else branch within fat_tolower, replace it with a branchless bitwise operation. This can reduce the number of branch ~130 regarding to the test script[1]. Test size can also be reduced: $ ./scripts/bloat-o-meter vmlinux_old vmlinux_new add/remove: 0/0 grow/shrink: 0/1 up/down: 0/-68 (-68) Function old new delta fat_parse_short 1901 1833 -68 Total: Before=3D22471023, After=3D22470955, chg -0.00% Signed-off-by: I Hsin Cheng --- [1]: static inline unsigned char old_tolower(unsigned char c) { return ((c >=3D 'A') && (c <=3D 'Z')) ? c+32 : c; } static inline unsigned char new_tolower(unsigned char c) { return c | 0x20; } int main(void) { for (unsigned char i =3D 0; i < 26; i++) { if (old_tolower('a' + i) !=3D old_tolower('A' + i)) return 1; } return 0; } Utilize perf to profile the difference when using old_tolower() and new_tolower(). $ perf stat -e branches,branch-misses --repeat 100 ./old Performance counter stats for './old': 2,6302 branches:u 2334 branch-misses:u 0.000754710 seconds time elapsed 0.000000000 seconds user 0.000804000 seconds sys $ perf stat -e branches,branch-misses --repeat 100 ./new Performance counter stats for './main': 2,6172 branches:u 2338 branch-misses:u 0.000782670 seconds time elapsed 0.000853000 seconds user 0.000000000 seconds sys Best regards, I Hsin Cheng --- fs/fat/dir.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/fat/dir.c b/fs/fat/dir.c index acbec5bdd521..77d212b4d4db 100644 --- a/fs/fat/dir.c +++ b/fs/fat/dir.c @@ -35,7 +35,7 @@ =20 static inline unsigned char fat_tolower(unsigned char c) { - return ((c >=3D 'A') && (c <=3D 'Z')) ? c+32 : c; + return c | 0x20; } =20 static inline loff_t fat_make_i_pos(struct super_block *sb, --=20 2.43.0