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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 77248CAC58E for ; Thu, 11 Sep 2025 18:15:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=06QEBt7vQMuCRYFVKDqYDii0jEZZNEOypNRSRw/R+dM=; b=Un9fHnVMcabJJD04VC6DM/1dxk zN80V60UynpFpN9IAJgG4mYAJkg7j8NzbLBlvDX6eoWn0TlideVWa/h3dlEQfvWZnH6mg8b0jqgcQ 2QHIy7/7oyNvVD91m/yqV4QahmUrk6kvvlg6XOZ/VBSt2M3t/BqJNhYqLd/eU3GTDZ1eGA+6KLcxN 0jTMHGrRNwM8HDcWqRWrwxZSfB2ptaxC0sREQjlEsf9i7fZOwk/ML/HK7FmiNgbhf2Ql/8XUJdRsK dSncFvvaO5W63Sd3x1C0focCG8q1zYerLD2UoAgcIjHqlLJvHoU1I2VKpLmRKTHwDebsNlNgQ2bed 5VJDmGRg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwlpg-00000004g2j-27yt; Thu, 11 Sep 2025 18:15:44 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwlpc-00000004fzb-43KY for linux-nvme@lists.infradead.org; Thu, 11 Sep 2025 18:15:43 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 2EF6D404B8; Thu, 11 Sep 2025 18:15:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8CC65C4CEF0; Thu, 11 Sep 2025 18:15:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1757614540; bh=a2Lob0n3/+GCVE61Fr7ySrkcY2m5OqzFFOAuvId4MiE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=YHF/RmRFumOOHkEnaB3xMYiqo0WcAPOUsR5NQ2XhQl2SJLAVBfc3/wjdHBHX8Wmbe KQVdxrNGKmWY3qjbhOJzzbYoQ2Q5sjebQoSSnx7vv4VBXx0lAc1fDEKsY760hrlSnB cw0Cc6hS1Ykvt7RXoXZHMCn8MkIP3zzIZQxrLMkYrj7Yqnd5FYs9DRrBQBYLsM9/i5 Ttq9vEAAXQhJPUxn4tJq3w2kSNphEY2nNwbwJlSRhVN8rrpjajtaojIRtId1AT7kxM nrIuRYtF5Z6Y8vUInleEY8memGNegfHCnpeDFpjJm5uAL8eDpW7AqF7lVG6duhuZ0j ioWusQwGr+YtA== Date: Thu, 11 Sep 2025 11:14:18 -0700 From: Eric Biggers To: Guan-Chun Wu <409411716@gms.tku.edu.tw> Cc: akpm@linux-foundation.org, axboe@kernel.dk, ceph-devel@vger.kernel.org, hch@lst.de, home7438072@gmail.com, idryomov@gmail.com, jaegeuk@kernel.org, kbusch@kernel.org, linux-fscrypt@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, sagi@grimberg.me, tytso@mit.edu, visitorckw@gmail.com, xiubli@redhat.com Subject: Re: [PATCH v2 1/5] lib/base64: Replace strchr() for better performance Message-ID: <20250911181418.GB1376@sol> References: <20250911072925.547163-1-409411716@gms.tku.edu.tw> <20250911073204.574742-1-409411716@gms.tku.edu.tw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250911073204.574742-1-409411716@gms.tku.edu.tw> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250911_111541_060011_C617AF9D X-CRM114-Status: GOOD ( 21.84 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On Thu, Sep 11, 2025 at 03:32:04PM +0800, Guan-Chun Wu wrote: > From: Kuan-Wei Chiu > > The base64 decoder previously relied on strchr() to locate each > character in the base64 table. In the worst case, this requires > scanning all 64 entries, and even with bitwise tricks or word-sized > comparisons, still needs up to 8 checks. > > Introduce a small helper function that maps input characters directly > to their position in the base64 table. This reduces the maximum number > of comparisons to 5, improving decoding efficiency while keeping the > logic straightforward. > > Benchmarks on x86_64 (Intel Core i7-10700 @ 2.90GHz, averaged > over 1000 runs, tested with KUnit): > > Decode: > - 64B input: avg ~1530ns -> ~126ns (~12x faster) > - 1KB input: avg ~27726ns -> ~2003ns (~14x faster) > > Signed-off-by: Kuan-Wei Chiu > Co-developed-by: Guan-Chun Wu <409411716@gms.tku.edu.tw> > Signed-off-by: Guan-Chun Wu <409411716@gms.tku.edu.tw> > --- > lib/base64.c | 17 ++++++++++++++++- > 1 file changed, 16 insertions(+), 1 deletion(-) > > diff --git a/lib/base64.c b/lib/base64.c > index b736a7a43..9416bded2 100644 > --- a/lib/base64.c > +++ b/lib/base64.c > @@ -18,6 +18,21 @@ > static const char base64_table[65] = > "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"; > > +static inline const char *find_chr(const char *base64_table, char ch) > +{ > + if ('A' <= ch && ch <= 'Z') > + return base64_table + ch - 'A'; > + if ('a' <= ch && ch <= 'z') > + return base64_table + 26 + ch - 'a'; > + if ('0' <= ch && ch <= '9') > + return base64_table + 26 * 2 + ch - '0'; > + if (ch == base64_table[26 * 2 + 10]) > + return base64_table + 26 * 2 + 10; > + if (ch == base64_table[26 * 2 + 10 + 1]) > + return base64_table + 26 * 2 + 10 + 1; > + return NULL; > +} > + > /** > * base64_encode() - base64-encode some binary data > * @src: the binary data to encode > @@ -78,7 +93,7 @@ int base64_decode(const char *src, int srclen, u8 *dst) > u8 *bp = dst; > > for (i = 0; i < srclen; i++) { > - const char *p = strchr(base64_table, src[i]); > + const char *p = find_chr(base64_table, src[i]); > > if (src[i] == '=') { > ac = (ac << 6); But this makes the contents of base64_table no longer be used, except for entries 62 and 63. So this patch doesn't make sense. Either we should actually use base64_table, or we should remove base64_table and do the mapping entirely in code. - Eric