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=-6.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 9E690C43469 for ; Sun, 20 Sep 2020 11:07:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6A28E20EDD for ; Sun, 20 Sep 2020 11:07:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726360AbgITLHY (ORCPT ); Sun, 20 Sep 2020 07:07:24 -0400 Received: from mail.baikalelectronics.com ([87.245.175.226]:53208 "EHLO mail.baikalelectronics.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726267AbgITLHW (ORCPT ); Sun, 20 Sep 2020 07:07:22 -0400 Received: from localhost (unknown [127.0.0.1]) by mail.baikalelectronics.ru (Postfix) with ESMTP id E64828030718; Sun, 20 Sep 2020 11:00:45 +0000 (UTC) X-Virus-Scanned: amavisd-new at baikalelectronics.ru Received: from mail.baikalelectronics.ru ([127.0.0.1]) by localhost (mail.baikalelectronics.ru [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id fpkgHK4YMOV0; Sun, 20 Sep 2020 14:00:45 +0300 (MSK) From: Serge Semin To: Thomas Bogendoerfer CC: Serge Semin , Serge Semin , Alexey Malahov , Pavel Parkhomenko , Vadim Vlasov , "Maciej W . Rozycki" , , Subject: [PATCH 0/2] mips: Introduce some IO-accessors optimizations Date: Sun, 20 Sep 2020 14:00:08 +0300 Message-ID: <20200920110010.16796-1-Sergey.Semin@baikalelectronics.ru> MIME-Version: 1.0 Content-Transfer-Encoding: 7BIT Content-Type: text/plain; charset=US-ASCII X-ClientProxiedBy: MAIL.baikal.int (192.168.51.25) To mail (192.168.51.25) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It has been discovered that on our MIPS P5600-based CPU the IO accessors aren't that rapid as they could be even taking into account a relatively slow AXI2APB bridge embedded into the system interconnect. Turned out we can introduce two types of optimizations. First we can remove the execution barriers from the relaxed IO-accessors as our CPU conforms to the MIPS Coherency Protocol Specification [1, 2]. Of course it also concerns the IO interconnect implementation. So in accordance with [3] we suggest to remove the barriers at least for the platforms which conform the specification the same way as ours. Second there is a dedicated Coherency Manager control register, which can be also used to tune the IO methods up. For some reason it hasn't been added to the MIPS arch code so far, while it provides flags for instance to speed the SYNC barrier for the platforms with non-re-ordering IO interconnect, to set the cache ops serialization limits, enable the speculative reads, etc. For now we suggest to add just the macro with the CM2 GCR_CONTROL register accessors and fields description. So any platform could use it to activate the corresponding optimization. Our platform-wise we'll do this in the framework of our Baikal-T1 platform code in the prom_init() method. [1] MIPS Coherence Protocol Specification, Document Number: MD00605, Revision 01.01. September 14, 2015, 4.2 Execution Order Behavior, p. 33 [2] MIPS Coherence Protocol Specification, Document Number: MD00605, Revision 01.01. September 14, 2015, 4.8.1 IO Device Access, p. 58 [3] "LINUX KERNEL MEMORY BARRIERS", Documentation/memory-barriers.txt, Section "KERNEL I/O BARRIER EFFECTS" Signed-off-by: Serge Semin Cc: Alexey Malahov Cc: Pavel Parkhomenko Cc: Vadim Vlasov Cc: Maciej W. Rozycki Cc: linux-mips@vger.kernel.org Cc: linux-kernel@vger.kernel.org Serge Semin (2): mips: Add strong UC ordering config mips: Introduce MIPS CM2 GCR Control register accessors arch/mips/Kconfig | 8 ++++++++ arch/mips/include/asm/io.h | 20 ++++++++++---------- arch/mips/include/asm/mips-cm.h | 15 +++++++++++++++ 3 files changed, 33 insertions(+), 10 deletions(-) -- 2.27.0