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 18524C0015E for ; Sun, 16 Jul 2023 17:03:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230129AbjGPRD3 (ORCPT ); Sun, 16 Jul 2023 13:03:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56956 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230047AbjGPRDX (ORCPT ); Sun, 16 Jul 2023 13:03:23 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4716BE5D for ; Sun, 16 Jul 2023 10:03:22 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id C513460DCB for ; Sun, 16 Jul 2023 17:03:21 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id E8391C433C8; Sun, 16 Jul 2023 17:03:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689527001; bh=20Zikv72OY76YPWE++4/3jVTe/sLWDTAfsZqK7N92KQ=; h=From:To:Cc:Subject:Date:From; b=Y7tUXlqTb2RTqjU/5X6XsYUAKr/1DDq7xMzby0BIFbpXmiQLOK8k8LS+kbQS/qrfJ 1SZysyfCHvFm1K/x5nW1nCrAkICcHzkrG7y8zmrTLEm733ySdb33bfCO+63pDhHivv IpOeg2jLQhicVR/g7jrMR/bANwzH6CDbvmbRHErQeK589svbW0w4wqp0esok7DLphh NKWMVyOTZtmkEcOMbMavx2rnEH3553pfJBQaOXqBy9aeJhqK2NYxL9U/Zysl2ml7pz 0s7csg7Xp0mVfYdatvdojnWSjKsoJJYIWbVVgTgTlQ6o5FnJeUml62SyglnrDg2fny c/xR76ujLxVpQ== From: Jisheng Zhang To: Paul Walmsley , Palmer Dabbelt , Albert Ou Cc: linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH v2 0/2] riscv: Reduce ARCH_KMALLOC_MINALIGN to 8 Date: Mon, 17 Jul 2023 00:51:45 +0800 Message-Id: <20230716165147.1897-1-jszhang@kernel.org> X-Mailer: git-send-email 2.40.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently, riscv defines ARCH_DMA_MINALIGN as L1_CACHE_BYTES, I.E 64Bytes, if CONFIG_RISCV_DMA_NONCOHERENT=y. To support unified kernel Image, usually we have to enable CONFIG_RISCV_DMA_NONCOHERENT, thus it brings some bad effects to coherent platforms: Firstly, it wastes memory, kmalloc-96, kmalloc-32, kmalloc-16 and kmalloc-8 slab caches don't exist any more, they are replaced with either kmalloc-128 or kmalloc-64. Secondly, larger than necessary kmalloc aligned allocations results in unnecessary cache/TLB pressure. This issue also exists on arm64 platforms. From last year, Catalin tried to solve this issue by decoupling ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN, limiting kmalloc() minimum alignment to dma_get_cache_alignment() and replacing ARCH_KMALLOC_MINALIGN usage in various drivers with ARCH_DMA_MINALIGN etc.[1] One fact we can make use of for riscv: if the CPU doesn't support ZICBOM or T-HEAD CMO, we know the platform is coherent. Based on Catalin's work and above fact, we can easily solve the kmalloc align issue for riscv: we can override dma_get_cache_alignment(), then let it return ARCH_DMA_MINALIGN at the beginning and return 1 once we know the underlying HW neither supports ZICBOM nor supports T-HEAD CMO. So what about if the CPU supports ZICBOM and T-HEAD CMO, but all the devices are dma coherent? Well, we use ARCH_DMA_MINALIGN as the kmalloc minimum alignment, nothing changed in this case. This case can be improved in the future. After this patch, a simple test of booting to a small buildroot rootfs on qemu shows: kmalloc-96 5041 5041 96 ... kmalloc-64 9606 9606 64 ... kmalloc-32 5128 5128 32 ... kmalloc-16 7682 7682 16 ... kmalloc-8 10246 10246 8 ... So we save about 1268KB memory. The saving will be much larger in normal OS env on real HW platforms. patch1 allows kmalloc() caches aligned to the smallest value. patch2 enables DMA_BOUNCE_UNALIGNED_KMALLOC. After this series: As for coherent platforms, kmalloc-{8,16,32,96} caches come back on coherent both RV32 and RV64 platforms, I.E !ZICBOM and !THEAD_CMO. As for noncoherent RV32 platforms, nothing changed. As for noncoherent RV64 platforms, I.E either ZICBOM or THEAD_CMO, the above kmalloc caches also come back if > 4GB memory or users pass "swiotlb=mmnn,force" to force swiotlb creation if <= 4GB memory. How much mmnn should be depends on the specific platform, it need to be tried and tested all possible usage case on the specific hardware. For example, I can use the minimal I/O TLB slabs on Sipeed M1S Dock. [1] Link: https://lore.kernel.org/linux-arm-kernel/20230524171904.3967031-1-catalin.marinas@arm.com/ Since v1 - remove preparation patches since they have been merged - adjust Kconfig entry to keep entries sorted - add new function riscv_set_dma_cache_alignment() to set the dma_cache_alignment var. Jisheng Zhang (2): riscv: allow kmalloc() caches aligned to the smallest value riscv: enable DMA_BOUNCE_UNALIGNED_KMALLOC for !dma_coherent arch/riscv/Kconfig | 1 + arch/riscv/include/asm/cache.h | 14 ++++++++++++++ arch/riscv/include/asm/cacheflush.h | 2 ++ arch/riscv/kernel/setup.c | 1 + arch/riscv/mm/dma-noncoherent.c | 8 ++++++++ 5 files changed, 26 insertions(+) -- 2.40.1