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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 5C62FC432C0 for ; Mon, 2 Dec 2019 13:51:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 385D72053B for ; Mon, 2 Dec 2019 13:51:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727503AbfLBNvM (ORCPT ); Mon, 2 Dec 2019 08:51:12 -0500 Received: from foss.arm.com ([217.140.110.172]:54724 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727451AbfLBNvL (ORCPT ); Mon, 2 Dec 2019 08:51:11 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CED6130E; Mon, 2 Dec 2019 05:51:10 -0800 (PST) Received: from [10.1.196.37] (e121345-lin.cambridge.arm.com [10.1.196.37]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 598313F68E; Mon, 2 Dec 2019 05:51:09 -0800 (PST) Subject: Re: [PATCH v1] clk: Convert managed get functions to devm_add_action API To: Marc Gonzalez , Dmitry Torokhov , Bjorn Andersson Cc: Kuninori Morimoto , Stephen Boyd , Michael Turquette , LKML , Sudip Mukherjee , Russell King , Guenter Roeck , linux-clk , Linux ARM References: <3d8a58bf-0814-1ec1-038a-10a20b9646ad@free.fr> <20191128185630.GK82109@yoga> <20191202014237.GR248138@dtor-ws> From: Robin Murphy Message-ID: Date: Mon, 2 Dec 2019 13:51:08 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-clk-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-clk@vger.kernel.org On 02/12/2019 9:25 am, Marc Gonzalez wrote: > On 02/12/2019 02:42, Dmitry Torokhov wrote: > >> On Thu, Nov 28, 2019 at 10:56:30AM -0800, Bjorn Andersson wrote: >> >>> On Tue 26 Nov 08:13 PST 2019, Marc Gonzalez wrote: >>> >>>> Date: Tue, 26 Nov 2019 13:56:53 +0100 >>>> >>>> Using devm_add_action_or_reset() produces simpler code and smaller >>>> object size: >>>> >>>> 1 file changed, 16 insertions(+), 46 deletions(-) >>>> >>>> text data bss dec hex filename >>>> - 1797 80 0 1877 755 drivers/clk/clk-devres.o >>>> + 1499 56 0 1555 613 drivers/clk/clk-devres.o >>>> >>>> Signed-off-by: Marc Gonzalez >>> >>> Looks neat >>> >>> Reviewed-by: Bjorn Andersson >> >> This however increases the runtime costs as each custom action cost us >> an extra pointer. Given that in a system we likely have many clocks >> managed by devres, I am not sure that this code savings is actually >> gives us overall win. It might still, I just want to understand how we >> are allocating/packing devres structures. > > I'm not 100% sure what you are saying. You reduce the text size by a constant amount, at the cost of allocating twice as much runtime data per clock (struct action_devres vs. void*). Assuming 64-bit pointers, that means that in principle your ~320-byte saving would be cancelled out at ~40 managed clocks. However, that's also assuming that the minimum allocation granularity is no larger than a single pointer, which generally isn't true, so in reality it depends on whether the difference in data pushes the total struct devres allocation over the next ARCH_KMALLOC_MINALIGN boundary - if it doesn't, the difference comes entirely for free; if it does, the memory cost tradeoff gets even worse. Robin. > Are you arguing that the proposed patch increases the run-time cost of > devm_clk_put() so much that the listed improvements (simpler source code, > smaller object size) are not worth it? > > AFAIU, the release action is only called > - explicitly, when devm_clk_put() is called > - implicitly, when the device is removed > > How often are clocks removed? > > In hot code-path (called hundreds of times per second) it makes sense to > write more complex code, to shave a few cycles every iteration. But in > cold code-path, I think it's better to write short/simple code. > > Regards. > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >