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=-6.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 279F6C433ED for ; Fri, 14 May 2021 12:24:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0049061285 for ; Fri, 14 May 2021 12:24:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233014AbhENMZM (ORCPT ); Fri, 14 May 2021 08:25:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:39692 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232968AbhENMZL (ORCPT ); Fri, 14 May 2021 08:25:11 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 800DA613CD; Fri, 14 May 2021 12:24:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1620995040; bh=wbxGv9t6GbRKjxv6rSslyvniGKsYirDLOL8luJLhqnk=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=U8RD4a6z1w6XaGa8ekohGmVHORARKCNldy0gUnyY2EqA4yJIydt/e79qIxr1+UoyW VUC877n7ZwbBEK6O7s8oDpWSl3Ycbe9UEM6sXBZnRvSCMhVSnsu+IEJUaLVbCnEDZd hJR0tbTj7eeAAa81AzZizDS42VIq3Oc8JZT7q/C1k2wuSRZIm3ePWQBeYaeta0ZdYj kjNLiKAppuu/sn3XW5v1pndVul0Kyn+cxoxbmrVJ86k6NKvsxbr1AQQpfOCHEZ5fEG JZP1QHPgOEvsdanB/NuSDHkvd/N83HebpVEsUfIL6PWCtPUzKZDZyVFUlwRsshqVsJ 3GexNN4/yWKrA== Received: by mail-ot1-f54.google.com with SMTP id v19-20020a0568301413b0290304f00e3d88so5143328otp.4; Fri, 14 May 2021 05:24:00 -0700 (PDT) X-Gm-Message-State: AOAM531d3+9D9XeJhUn54U5tjSWsha9vQ06jhPdHw3L1OICH8qH/KG5H XScxqN64Ii0oDV2rb78cM2Hdfbfr/jNxtLzU4JU= X-Google-Smtp-Source: ABdhPJzROl7Fjyj6XasZO8+BKHJUHE5O/PN10u+bqcgEIYgEvw0o6mBqLsX7pHbqhU/n94ZuitW4NB9Oem1Vvp+o28k= X-Received: by 2002:a9d:222a:: with SMTP id o39mr38555525ota.246.1620995039855; Fri, 14 May 2021 05:23:59 -0700 (PDT) MIME-Version: 1.0 References: <20210514100106.3404011-1-arnd@kernel.org> <20210514100106.3404011-4-arnd@kernel.org> <3d70eb2a-2969-197e-63e8-f3e0a6a8ddd8@physik.fu-berlin.de> In-Reply-To: <3d70eb2a-2969-197e-63e8-f3e0a6a8ddd8@physik.fu-berlin.de> From: Arnd Bergmann Date: Fri, 14 May 2021 14:22:58 +0200 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH v2 03/13] sh: remove unaligned access for sh4a To: John Paul Adrian Glaubitz Cc: linux-arch , Linus Torvalds , Vineet Gupta , Yoshinori Sato , Rich Felker , Linux-sh list , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-sh@vger.kernel.org On Fri, May 14, 2021 at 12:34 PM John Paul Adrian Glaubitz wrote: > > Hi Arnd! > > On 5/14/21 12:00 PM, Arnd Bergmann wrote: > > Unlike every other architecture, sh4a uses an inline asm implementation > > for get_unaligned(). I have shown that this produces better object > > code than the asm-generic version. However, there are very few users of > > arch/sh/ overall, and most of those seem to use sh4 rather than sh4a CPU > > cores, so it seems not worth keeping the complexity in the architecture > > independent code. > > My Renesas SH4-Boards actually run an sh4a-Kernel, not an sh4-Kernel: > > root@tirpitz:~> uname -a > Linux tirpitz 5.11.0-rc4-00012-g10c03c5bf422 #161 PREEMPT Mon Jan 18 21:10:17 CET 2021 sh4a GNU/Linux > root@tirpitz:~> > > So, if this change reduces performance on sh4a, I would rather not merge it. It only makes a difference in very specific scenarios in which unaligned accesses are done in a fast path, e.g. when forwarding network packet at a high rate on a big-endian kernel (little-endian kernels wouldn't run into this on IP headers). If you have a use case for this machine on which the you can show a performance regression, I can add a patch on top to put the optimized sh4a get_unaligned_le32() back. Dropping this patch altogether would make the series much more complex because most of the associated code gets removed in the end. As I mentioned, supporting "movua" in the compiler likely has a much larger impact on performance, as it would also help in user space, and it should improve the networking case on little-endian kernels by replacing the four separate byte loads/shift pairs with a movua plus a byteswap. Not sure if there are gcc developers that have an active interest in sh4a support any more. Arnd