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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C55A4C4167B for ; Sat, 2 Dec 2023 11:54:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232642AbjLBLkl (ORCPT ); Sat, 2 Dec 2023 06:40:41 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36960 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229451AbjLBLki (ORCPT ); Sat, 2 Dec 2023 06:40:38 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3B82218C for ; Sat, 2 Dec 2023 03:40:42 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C2E4CC433C9; Sat, 2 Dec 2023 11:40:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1701517241; bh=DaUNBnJudQtx/0ecN0kp9sHu1Y4tp3r/amh8XiErTXw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XxP7NmO7pW5CZG2wIqTdiWAbz/p7Cb69Elg+6qaP8cxRpDnbg7ygo36gqVDhTE1K/ 9ky2d7U5rmERCih5gsM/OV7/Euy7yG9zru8jDb1Wo8AaCAmx16YQ8OWUrgYiZbRZU2 j3+lowrobiVTpvQ2b6+uTV66aCyeHH+QBwj9f/5P350NydZGYMw+Zqj8RrAblu9VK9 5QbS1cVL3ev75+j1EMolBAA/CKFvjCSTTpRLmXILv7TSu/sdW4GQJdCU2fgWr+hTQd frwOzSl7jv2TwAURI820vGSlC+0FQ9hxApvrrEHa/s+BsP9WMC1YSfh+TShW4XOF4M ZdQ7qFC8qFLAw== Date: Sat, 2 Dec 2023 19:28:10 +0800 From: Jisheng Zhang To: Paul Walmsley , Palmer Dabbelt , Albert Ou Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 0/2] riscv: enable EFFICIENT_UNALIGNED_ACCESS and DCACHE_WORD_ACCESS Message-ID: References: <20231202111822.3569-1-jszhang@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20231202111822.3569-1-jszhang@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Dec 02, 2023 at 07:18:20PM +0800, Jisheng Zhang wrote: > Some riscv implementations such as T-HEAD's C906, C908, C910 and C920 > supports efficient unaligned access, for performance reason we want > to enable HAVE_EFFICIENT_UNALIGNED_ACCESS on these platforms. To > avoid performance regressions on other non efficient unaligned access > platforms, HAVE_EFFICIENT_UNALIGNED_ACCESS can't be globaly selected. > > To solve this problem, runtime code patching based on the detected > speed is a good solution. But that's not easy, it involves lots of > work to modify vairous subsystems such as net, mm, lib and so on. > This can be done step by step. Adding something as below here can make the series more clear: So let's take an easier solution: add support to efficient unaligned access and hide the support under NONPORTABLE. > > patch1 introduces RISCV_EFFICIENT_UNALIGNED_ACCESS which depends on > NONPORTABLE, if users know during config time that the kernel will be > only run on those efficient unaligned access hw platforms, they can > enable it. Obviously, generic unified kernel Image should enable it. typo: s/should/shouldn't > > patch2 adds support DCACHE_WORD_ACCESS when MMU and > RISCV_EFFICIENT_UNALIGNED_ACCESS. > > Below test program and step shows how much performance can be improved: > > $ cat tt.c > #include > #include > #include > > #define ITERATIONS 1000000 > > #define PATH "123456781234567812345678123456781" > > int main(void) > { > unsigned long i; > struct stat buf; > > for (i = 0; i < ITERATIONS; i++) > stat(PATH, &buf); > > return 0; > } > > $ gcc -O2 tt.c > $ touch 123456781234567812345678123456781 > $ time ./a.out > > Per my test on T-HEAD C910 platforms, the above test performance is > improved by about 7.5%. > > > Jisheng Zhang (2): > riscv: introduce RISCV_EFFICIENT_UNALIGNED_ACCESS > riscv: select DCACHE_WORD_ACCESS for efficient unaligned access HW > > arch/riscv/Kconfig | 13 +++++++++++ > arch/riscv/include/asm/asm-extable.h | 15 ++++++++++++ > arch/riscv/include/asm/word-at-a-time.h | 23 ++++++++++++++++++ > arch/riscv/mm/extable.c | 31 +++++++++++++++++++++++++ > 4 files changed, 82 insertions(+) > > -- > 2.42.0 > > > _______________________________________________ > linux-riscv mailing list > linux-riscv@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-riscv