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 613DEEB64DC for ; Tue, 18 Jul 2023 14:51:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231590AbjGROvv (ORCPT ); Tue, 18 Jul 2023 10:51:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37040 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231442AbjGROvt (ORCPT ); Tue, 18 Jul 2023 10:51:49 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6062CA4 for ; Tue, 18 Jul 2023 07:51:48 -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 E596C615CE for ; Tue, 18 Jul 2023 14:51:47 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EDAF1C433C8; Tue, 18 Jul 2023 14:51:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1689691907; bh=gmjcvA7n5faDSrCMzbCX4megI4WqnvTMm5Hoj8Ds/LA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=JZ8IfIIk0SYNpmlwNXsBWnNAHXr/ZWod5/c666cBApDXFwrSCsVUQzaKEG2A0NdMv cg3FmVQPix8DgikdHM0CRLwbW7DNXZO3l5NvfwdOWsBdWUV20mt28HN1Bh0ck18saR MyU5cO4CS8hMD6EiL1VmSp7V0Y2ExoTaNH3/pwi3g4Ew/RzCXzJbu2R7EIUAx+i27i oXhMTseXhjezDRv3F1sklp5zSW8nlzLmsN2+FJoE3xxFP5D47eEi3s/GjuslHIC4qx ltLYqUo7AHk0/scqq++iQ+txIXHHxe1MJhaPqRNxo7R6kgNYyFGz0J+VF5M+4HCVpx 1VV64+V6wduXw== Date: Tue, 18 Jul 2023 22:40:11 +0800 From: Jisheng Zhang To: Conor Dooley Cc: Paul Walmsley , Palmer Dabbelt , Albert Ou , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/2] riscv: allow kmalloc() caches aligned to the smallest value Message-ID: References: <20230716165147.1897-1-jszhang@kernel.org> <20230716165147.1897-2-jszhang@kernel.org> <20230718-brook-engross-1e7c273facdb@spud> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230718-brook-engross-1e7c273facdb@spud> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 18, 2023 at 11:23:50AM +0100, Conor Dooley wrote: > Hey Jisheng, > > On Mon, Jul 17, 2023 at 12:51:46AM +0800, Jisheng Zhang wrote: > > 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. > > > > [1] Link: https://lore.kernel.org/linux-arm-kernel/20230524171904.3967031-1-catalin.marinas@arm.com/ > > In the future, > > Link: https://lore.kernel.org/linux-arm-kernel/20230524171904.3967031-1-catalin.marinas@arm.com/ [1] > > > Signed-off-by: Jisheng Zhang > > Change-Id: Ica249d0f8058a02bd4bc6543b4ffc2946a4734a2 > > How come this has ended up with a Change-ID? Checkpatch says this is > something to do with Gerrit & needs to be removed. Oops, when amending, I forgot to add "-n". And I thought only amending doesn't need to try checkpatch. Will fix it soon. Thank you. > > > --- > > 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 ++++++++ > > 4 files changed, 25 insertions(+) > > > > diff --git a/arch/riscv/include/asm/cache.h b/arch/riscv/include/asm/cache.h > > index d3036df23ccb..2174fe7bac9a 100644 > > --- a/arch/riscv/include/asm/cache.h > > +++ b/arch/riscv/include/asm/cache.h > > @@ -13,6 +13,7 @@ > > > > #ifdef CONFIG_RISCV_DMA_NONCOHERENT > > #define ARCH_DMA_MINALIGN L1_CACHE_BYTES > > +#define ARCH_KMALLOC_MINALIGN (8) > > #endif > > > > /* > > @@ -23,4 +24,17 @@ > > #define ARCH_SLAB_MINALIGN 16 > > #endif > > > > +#ifndef __ASSEMBLY__ > > + > > +#ifdef CONFIG_RISCV_DMA_NONCOHERENT > > +extern int dma_cache_alignment; > > +#define dma_get_cache_alignment dma_get_cache_alignment > > +static inline int dma_get_cache_alignment(void) > > +{ > > + return dma_cache_alignment; > > +} > > +#endif > > + > > +#endif /* __ASSEMBLY__ */ > > + > > #endif /* _ASM_RISCV_CACHE_H */ > > diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h > > index 8091b8bf4883..c640ab6f843b 100644 > > --- a/arch/riscv/include/asm/cacheflush.h > > +++ b/arch/riscv/include/asm/cacheflush.h > > @@ -55,8 +55,10 @@ void riscv_init_cbo_blocksizes(void); > > > > #ifdef CONFIG_RISCV_DMA_NONCOHERENT > > void riscv_noncoherent_supported(void); > > +void __init riscv_set_dma_cache_alignment(void); > > #else > > static inline void riscv_noncoherent_supported(void) {} > > +static inline void riscv_set_dma_cache_alignment(void) {} > > #endif > > > > /* > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c > > index 971fe776e2f8..027879b1557a 100644 > > --- a/arch/riscv/kernel/setup.c > > +++ b/arch/riscv/kernel/setup.c > > @@ -311,6 +311,7 @@ void __init setup_arch(char **cmdline_p) > > if (IS_ENABLED(CONFIG_RISCV_ISA_ZICBOM) && > > riscv_isa_extension_available(NULL, ZICBOM)) > > riscv_noncoherent_supported(); > > + riscv_set_dma_cache_alignment(); > > } > > > > static int __init topology_init(void) > > diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c > > index d51a75864e53..811227e54bbd 100644 > > --- a/arch/riscv/mm/dma-noncoherent.c > > +++ b/arch/riscv/mm/dma-noncoherent.c > > @@ -11,6 +11,8 @@ > > #include > > > > static bool noncoherent_supported __ro_after_init; > > +int dma_cache_alignment __ro_after_init = ARCH_DMA_MINALIGN; > > +EXPORT_SYMBOL(dma_cache_alignment); > > Why is this not EXPORT_SYMBOL_GPL()? > > Otherwise, this is generally good to me, thanks. > > Conor. > > > > > void arch_sync_dma_for_device(phys_addr_t paddr, size_t size, > > enum dma_data_direction dir) > > @@ -78,3 +80,9 @@ void riscv_noncoherent_supported(void) > > "Non-coherent DMA support enabled without a block size\n"); > > noncoherent_supported = true; > > } > > + > > +void __init riscv_set_dma_cache_alignment(void) > > +{ > > + if (!noncoherent_supported) > > + dma_cache_alignment = 1; > > +} > > -- > > 2.40.1 > >