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=-2.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,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 2EB04C43603 for ; Thu, 12 Dec 2019 19:10:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 023D521556 for ; Thu, 12 Dec 2019 19:10:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="DDCckX+5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730096AbfLLTKG (ORCPT ); Thu, 12 Dec 2019 14:10:06 -0500 Received: from mail-pj1-f68.google.com ([209.85.216.68]:41385 "EHLO mail-pj1-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730346AbfLLTKG (ORCPT ); Thu, 12 Dec 2019 14:10:06 -0500 Received: by mail-pj1-f68.google.com with SMTP id ca19so1449012pjb.8; Thu, 12 Dec 2019 11:10:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=/CFTvsuLouSL+b+ykFmdN8fLszmQshAka4tYRtpWxCg=; b=DDCckX+53jRup7lxzh/bxqu4w8WMEM7JfkNDE8ddbtmubhsPo4HzghREbieunEzc4N /QIPAlyEXZJpzbxaTi/10nLMDa2VjWS3gJv37yKhE9LNJVNy2mVKqq/QAOaZqPnDnqUI JGiiJtS9CXi/rZk6LP7urXNmhEgcbd9d9neOsGM0759DtGXJxFhvRqYZW0WivJwpCv/K Q2eqUU2ulZ32zGaWZ0ojcvhTNMi2R8RD0zyGSumPB/oCZbcQInbGOvCBYz5DNbmVfl3t YZFHzsIy/mTl3a9enQkCC7bg68f7N4oj8pajqNH3ytaqLgRJbHxLhxIg1QOQl2HpmsZu 4OeQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=/CFTvsuLouSL+b+ykFmdN8fLszmQshAka4tYRtpWxCg=; b=EAyPXDVCZyv3FvYov9MZAsQFrjmpEXucat0VTr/Ev6md8bgMBn9GQsNa6SWBf2GF6q 16xm5Ndr+dSCLFaBsDDmrE1ztOwHvzs3vzDM2qqL2SFhZX3t6r1ruKwjdZJGg96jyg/n qPQYDLc46ojaweapIKTIWTcPr8v06R0WwX0iZQvJYZR1MwBPcyzVuSR1rfX6JZHRb0k1 dZzidoXBAlMPiwbli80jTrfN6tWFWdWRZIwlq7ZMLOBMiOfXmDXQIj/pknrRRs1mUTuf jpR9dlYqkkkgT32gJ/fxhZM8FDMr9lywBswt1r/10CdBKbS/5K/TdmlYhKGlP7UfnfSD czIw== X-Gm-Message-State: APjAAAUKmNw7OY+OO6SmtJLnBCZq5fGry8YptZkVNti5jOquP6MWwyHF WDwO0kYaQ3H85AHjdfO1zhw= X-Google-Smtp-Source: APXvYqy80cGHOGC3vXShKkDjiLlNoD3iNKSNfr0cJkwWPHaK/hzVp8CcTB//JpDWpvEmMRR4xvjaSA== X-Received: by 2002:a17:902:7287:: with SMTP id d7mr11152811pll.17.1576177805515; Thu, 12 Dec 2019 11:10:05 -0800 (PST) Received: from dtor-ws ([2620:15c:202:201:3adc:b08c:7acc:b325]) by smtp.gmail.com with ESMTPSA id v29sm7466413pgl.88.2019.12.12.11.10.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 12 Dec 2019 11:10:04 -0800 (PST) Date: Thu, 12 Dec 2019 11:10:02 -0800 From: Dmitry Torokhov To: Robin Murphy Cc: Marc Gonzalez , Bjorn Andersson , Kuninori Morimoto , Stephen Boyd , Michael Turquette , LKML , Sudip Mukherjee , Russell King , Guenter Roeck , linux-clk , Linux ARM , x86 Subject: Re: [PATCH v1] clk: Convert managed get functions to devm_add_action API Message-ID: <20191212191002.GA101194@dtor-ws> References: <20191128185630.GK82109@yoga> <20191202014237.GR248138@dtor-ws> <20191211222829.GV50317@dtor-ws> <70528f77-ca10-01cd-153b-23486ce87d45@free.fr> <6a647c20-c2fa-f14c-256d-6516d0ad03b0@free.fr> <6ce49a67-8065-277b-5f80-ed47011e50d6@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6ce49a67-8065-277b-5f80-ed47011e50d6@arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-clk-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-clk@vger.kernel.org On Thu, Dec 12, 2019 at 06:15:16PM +0000, Robin Murphy wrote: > On 12/12/2019 4:59 pm, Marc Gonzalez wrote: > > 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) > > Ah yes, I failed to mentally preprocess the debug config :) > > > 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). > > I'm not sure it was a criticism so much as an observation of an aspect that > deserved consideration (certainly it was on my part, and I read Dmitry's "It > might still, ..." as implying the same). I'd say by this point it has been > thoroughly considered, and personally I'm now happy with the conclusion that > the kind of embedded platforms that will have many dozens of clocks are also > the kind that will tend to have enough padding to make it moot, and thus the > code simplification probably is worthwhile overall. I wonder if we could actually avoid allocating the data with ARCH_KMALLOC_MINALIGN in all the cases. It is definitely needed for the devm_k*alloc() group of functions as they are direct replacement for k*alloc() APIs that give users aligned memory, but for other data structures (clocks, regulators, etc, etc) it is not required. Thanks. -- Dmitry