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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 5057CC433E0 for ; Mon, 1 Jun 2020 07:22:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 26882206C3 for ; Mon, 1 Jun 2020 07:22:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Qy+GRsFw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727945AbgFAHWO (ORCPT ); Mon, 1 Jun 2020 03:22:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49494 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725935AbgFAHWN (ORCPT ); Mon, 1 Jun 2020 03:22:13 -0400 Received: from mail-vs1-xe42.google.com (mail-vs1-xe42.google.com [IPv6:2607:f8b0:4864:20::e42]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A38A0C061A0E; Mon, 1 Jun 2020 00:22:13 -0700 (PDT) Received: by mail-vs1-xe42.google.com with SMTP id o2so2163836vsr.0; Mon, 01 Jun 2020 00:22:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=LIgRN0QDBu4gnSn3TisqfMx5xMC/fpgZPP0eL7TYZo4=; b=Qy+GRsFwP59gROSPpwcSk+d4BmBdCEdjxVcnG89ETwVbaChC3CZGqNCjYA5q3zZEXV ftJjSX22++JyxqShjPrcs60ExBRV9rkg0po2DVvCYUGUQ+/Lln9ssEhgcKVqibq5h1QD 3GcB+VR5pmjymE7fc4kCi6UuBXGedcxGeKYY0JahfpNnaRtzua+jlXVyuPKz5eq95nyx FH5rsmTOlXiADyitE7Yo9XplyqzAHQ1AspJB0cypzPPGDXANPkzbpULgcPelQMQlpYkn q2rtZDeeH2pm1YHT1QiK+n+u+A7jM83OUkEtSD+uInIdVHUsPiVFys6kxdjnMNKzkX37 ++ig== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=LIgRN0QDBu4gnSn3TisqfMx5xMC/fpgZPP0eL7TYZo4=; b=ek40dg9u6PY9p5yDFRjTOxpa6vDqCZFAN+FfzvCrm0BqPTd8VLD5yuw0tshuQgRzXL Z9Zws+lkEhm7OSHbOH1YyDg5gyzfmRRPOQ2d7Ijqb1fVekg6cdgo49j2aic5hGA+62zV YQOyIBm/HEPfJnbvnjCptoCEkZovXN7hWirJ9cwG5kJGOXeafaIhXuJy7dttDnThPQIJ OroiIQta9PqAexB/3Tsu1215a63tRdEdyInhO8GikbPLxN7hONQkHtTqXWOgkk9Ww1KW BCvvayr0MDm8B0lQpy20gRC7IDoUYEh6nFEqhvPxkH1aUcBOqaimPE2XStSxibQ3r2Y1 Dekw== X-Gm-Message-State: AOAM532eokaXmWqinM7c1K+1NwdseA2DRieP8YIj9LuyocXpOsMz8XyP Bmsx0ia+CepbDFkTqEKhKPn0mz5O04BjZnP1gxc= X-Google-Smtp-Source: ABdhPJzIA1FGKrVz+9UgvnCvE4qHbM8WwKnt0yzT0Ej9MwEf3XXL3bZ9GG5bYf4/kar44nR6s2ZBVVKbKsVOWbpBIWw= X-Received: by 2002:a05:6102:a17:: with SMTP id t23mr9115865vsa.62.1590996132886; Mon, 01 Jun 2020 00:22:12 -0700 (PDT) MIME-Version: 1.0 References: <20200529141100.37519-1-pilgrimtao@gmail.com> In-Reply-To: From: Tao pilgrim Date: Mon, 1 Jun 2020 15:22:01 +0800 Message-ID: Subject: Re: [PATCH v2] blkdev: Replace blksize_bits() with ilog2() To: Jens Axboe Cc: hch@lst.de, sth@linux.ibm.com, viro@zeniv.linux.org.uk, clm@fb.com, jaegeuk@kernel.org, hch@infradead.org, Mark Fasheh , dhowells@redhat.com, balbi@kernel.org, damien.lemoal@wdc.com, bvanassche@acm.org, ming.lei@redhat.com, martin.petersen@oracle.com, satyat@google.com, chaitanya.kulkarni@wdc.com, houtao1@huawei.com, asml.silence@gmail.com, ajay.joshi@wdc.com, linux-kernel@vger.kernel.org, Muchun Song , hoeppner@linux.ibm.com, heiko.carstens@de.ibm.com, gor@linux.ibm.com, borntraeger@de.ibm.com, linux-s390@vger.kernel.org, sagi@grimberg.me, linux-nvme@lists.infradead.org, gregkh@linuxfoundation.org, linux-usb@vger.kernel.org, Josef Bacik , dsterba@suse.com, linux-btrfs@vger.kernel.org, chao@kernel.org, linux-f2fs-devel@lists.sourceforge.net, darrick.wong@oracle.com, linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, jlbec@evilplan.org, joseph.qi@linux.alibaba.com, ocfs2-devel@oss.oracle.com, deepa.kernel@gmail.com Content-Type: text/plain; charset="UTF-8" Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Fri, May 29, 2020 at 10:13 PM Jens Axboe wrote: > > On 5/29/20 8:11 AM, Kaitao Cheng wrote: > > There is a function named ilog2() exist which can replace blksize. > > The generated code will be shorter and more efficient on some > > architecture, such as arm64. And ilog2() can be optimized according > > to different architecture. > > When you posted this last time, I said: > > "I like the simplification, but do you have any results to back up > that claim? Is the generated code shorter? Runs faster?" > Hi Jens Axboe: I did a test on ARM64. unsigned int ckt_blksize(int size) { return blksize_bits(size); } unsigned int ckt_ilog2(int size) { return ilog2(size); } When I compiled it into assembly code, I got the following result, 0000000000000088 : 88: 2a0003e8 mov w8, w0 8c: 321d03e0 orr w0, wzr, #0x8 90: 11000400 add w0, w0, #0x1 94: 7108051f cmp w8, #0x201 98: 53017d08 lsr w8, w8, #1 9c: 54ffffa8 b.hi 90 a0: d65f03c0 ret a4: d503201f nop 00000000000000a8 : a8: 320013e8 orr w8, wzr, #0x1f ac: 5ac01009 clz w9, w0 b0: 4b090108 sub w8, w8, w9 b4: 7100001f cmp w0, #0x0 b8: 5a9f1100 csinv w0, w8, wzr, ne bc: d65f03c0 ret The generated code of ilog2 is shorter , and runs faster > which you handily ignored, yet sending out a new version. I'm not > going to apply this without justification, your commit message is > handwavy at best. > Do I need to write the test content into commit message? -- Yours, Kaitao Cheng