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=-2.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 64158C43603 for ; Thu, 12 Dec 2019 16:59:14 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3694D2173E for ; Thu, 12 Dec 2019 16:59:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="D88lA2uL" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3694D2173E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=free.fr Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date: Message-ID:From:References:To:Subject:Reply-To:Content-ID:Content-Description :Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=oblh6EZkFab2AYuMZwHeWiDLlNb36RDRKjisbxwWEo4=; b=D88lA2uLCqWO9p OEcH6IOfXd+RjMq2I80F6sUQozoe3oCH4+ZAQFiTGCDftlsyzFJmJ2GOcgmFYGLjUsSTZLKEvOEH9 fj98rrQGiK63Wx9fcUuUadQSNP7JXqO4bUA1UYTocA0uXls75VPrir04/aF4yw/k1ie6ylN3zdw3/ oxljl5pFmMMDQ8Gb3BcOCoDD8ce8pIxYalYSHytP+7w0Y9flmzUnPt57zI7Rru5kSYG4ozvL9mPGF ptFZMKeGJq7ay0buE8q/GBpyuWEtAZD2AXHRd5+8gAqZR98BzzxT1NEPTSpFfpoWc+7eUVr6bqT9/ 5QOxaHDyGZddARX4nucw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1ifRo1-0007WV-FU; Thu, 12 Dec 2019 16:59:13 +0000 Received: from ns.iliad.fr ([212.27.33.1]) by bombadil.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1ifRny-0007Sp-5k for linux-arm-kernel@lists.infradead.org; Thu, 12 Dec 2019 16:59:12 +0000 Received: from ns.iliad.fr (localhost [127.0.0.1]) by ns.iliad.fr (Postfix) with ESMTP id 60C5E202D4; Thu, 12 Dec 2019 17:59:04 +0100 (CET) Received: from [192.168.108.51] (freebox.vlq16.iliad.fr [213.36.7.13]) by ns.iliad.fr (Postfix) with ESMTP id 4785D200E6; Thu, 12 Dec 2019 17:59:04 +0100 (CET) Subject: Re: [PATCH v1] clk: Convert managed get functions to devm_add_action API To: Robin Murphy , Dmitry Torokhov References: <3d8a58bf-0814-1ec1-038a-10a20b9646ad@free.fr> <20191128185630.GK82109@yoga> <20191202014237.GR248138@dtor-ws> <20191211222829.GV50317@dtor-ws> <70528f77-ca10-01cd-153b-23486ce87d45@free.fr> From: Marc Gonzalez Message-ID: <6a647c20-c2fa-f14c-256d-6516d0ad03b0@free.fr> Date: Thu, 12 Dec 2019 17:59:04 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Virus-Scanned: ClamAV using ClamSMTP ; ns.iliad.fr ; Thu Dec 12 17:59:04 2019 +0100 (CET) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191212_085910_516151_9C765575 X-CRM114-Status: GOOD ( 11.60 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kuninori Morimoto , Stephen Boyd , Michael Turquette , x86 , linux-clk , LKML , Bjorn Andersson , Russell King , Linux ARM , Sudip Mukherjee , Guenter Roeck Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 12/12/2019 15:47, Robin Murphy wrote: > On 12/12/2019 1:53 pm, Marc Gonzalez wrote: > >> On 11/12/2019 23:28, Dmitry Torokhov wrote: >> >>> On Wed, Dec 11, 2019 at 05:17:28PM +0100, Marc Gonzalez wrote: >>> >>>> What is the rationale for the devm_add_action API? >>> >>> For one-off and maybe complex unwind actions in drivers that wish to use >>> devm API (as mixing devm and manual release is verboten). Also is often >>> used when some core subsystem does not provide enough devm APIs. >> >> Thanks for the insight, Dmitry. Thanks to Robin too. >> >> This is what I understand so far: >> >> devm_add_action() is nice because it hides/factorizes the complexity >> of the devres API, but it incurs a small storage overhead of one >> pointer per call, which makes it unfit for frequently used actions, >> such as clk_get. >> >> Is that correct? >> >> My question is: why not design the API without the small overhead? > > Probably because on most architectures, ARCH_KMALLOC_MINALIGN is at > least as big as two pointers anyway, so this "overhead" should mostly be > free in practice. Plus the devres API is almost entirely about being > able to write simple robust code, rather than absolute efficiency - I > mean, struct devres itself is already 5 pointers large at the absolute > minimum ;) (3 pointers: 1 list_head + 1 function pointer) I'm confused. The first patch was criticized for potentially adding an extra pointer for every devm_clk_get (e.g. 800 bytes on a 64-bit platform with 100 clocks). Let's see. On arm64, ARCH_KMALLOC_MINALIGN is 128. So basically, a struct devres looks like this on arm64: list_head.next list_head.prev dr_release_t . . . 104 bytes of padding . . . data (flexible array) . . . padding up to 256 bytes Basically, on arm64, every struct devres occupies 256 bytes, most of it (typically 104 + 112 = 216) wasted as padding. Hmmm, given how many devm stuff goes on in a modern platform, there might be large savings to be had... Assuming 10,000 calls to devres_alloc_node(), we would be wasting ~2 MB of RAM. Not sure it's worth trying to save that? $ git grep '#define ARCH_DMA_MINALIGN' arch/arc/include/asm/cache.h:#define ARCH_DMA_MINALIGN SMP_CACHE_BYTES arch/arm/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/arm64/include/asm/cache.h:#define ARCH_DMA_MINALIGN (128) arch/c6x/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/csky/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/hexagon/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/m68k/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/microblaze/include/asm/page.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/mips/include/asm/mach-generic/kmalloc.h:#define ARCH_DMA_MINALIGN 128 arch/mips/include/asm/mach-ip32/kmalloc.h:#define ARCH_DMA_MINALIGN 32 arch/mips/include/asm/mach-ip32/kmalloc.h:#define ARCH_DMA_MINALIGN 128 arch/mips/include/asm/mach-tx49xx/kmalloc.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/nds32/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/nios2/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/parisc/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/powerpc/include/asm/page_32.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/sh/include/asm/page.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/unicore32/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES arch/xtensa/include/asm/cache.h:#define ARCH_DMA_MINALIGN L1_CACHE_BYTES Hmmm, how does arch/x86 do it? Regards. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel