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 4C1EFC433E2 for ; Mon, 15 Jun 2020 16:35:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 270A320679 for ; Mon, 15 Jun 2020 16:35:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="lIxkFBz4" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731068AbgFOQfK (ORCPT ); Mon, 15 Jun 2020 12:35:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57504 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730622AbgFOQfI (ORCPT ); Mon, 15 Jun 2020 12:35:08 -0400 Received: from mail-wr1-x443.google.com (mail-wr1-x443.google.com [IPv6:2a00:1450:4864:20::443]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9358EC061A0E; Mon, 15 Jun 2020 09:35:07 -0700 (PDT) Received: by mail-wr1-x443.google.com with SMTP id l11so17819122wru.0; Mon, 15 Jun 2020 09:35:07 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=5lQ7/lXKr17vodyRktD27IeUshUvPdaX3z7NooA/F6c=; b=lIxkFBz4V7PvO7vVgR/1G7SztwCxC+vE7xGy7iiI04gpvRrGz3fvI6WC2TlbheWbcA hVziL9UihaCcCbEfALSiVRaZEaoEWBDglQSV7TEf4br1zJMuX19hnyeWo2IBZjx1+F4T GNG5MSP4WRky8nQZ6FezVDnp8l/iUQelNogrAsqbUOnGnXMk1D2ga531EYXwTTm+Z32V zrhWCmNoWtFtobtHUq8eRx4yMvvhF+TR4xw4vOUFD5xk9BEliXendpGi3k62DLLehbVU AKog/oFVxhmYuZJZMkHqRqWZxcPbRUmS8YKBMXB7PROAR0Zse1agKmEZyIMnnkdkmczY vexA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=5lQ7/lXKr17vodyRktD27IeUshUvPdaX3z7NooA/F6c=; b=NSieIw2QkhC7AGri6LILIaNY4AntXJV60RgY9O5A/B2lvjTyudyRK3uP2wZi8tk3mV io5h84M+v5pbjT632U9cefLbnI//9shA9B44VhAqazUN1asD86gOFG3vBQ//oBXhj+3V JjKBKhMM08sgREZeVGbUhVvPmelq9CNKF4Ivvkbh28iCXSo3i5w4Wq3nzkTIgq1QpR/7 AZhjIsk+h6YCVo+45fx6mMK4pGb7Kk6uRo3PAPn4h4ms+1N+UCFFAoA//qc9csul/LE4 Tqif2r3fRyPLcQhBD25j6W9uffsU+upV1RpBQe2GO59F7zh5M5R9ZXtEgBmbj1NhuJBA BKnA== X-Gm-Message-State: AOAM532n8qAMP/6DXxccku/+UMm27Z2iZUyrB/bqzK9gk65t6KACoelA SNR10jvGugjF+3fIEKdNXNc= X-Google-Smtp-Source: ABdhPJx16P7DvzPCkCZaqX3CvQm6rK5GkXK/vM+JGs/qyiKtD3n7zer28P+ZWST4ukMKG0x0q4CynA== X-Received: by 2002:adf:ecc2:: with SMTP id s2mr32591979wro.60.1592238906258; Mon, 15 Jun 2020 09:35:06 -0700 (PDT) Received: from [10.230.188.43] ([192.19.223.252]) by smtp.gmail.com with ESMTPSA id d24sm67808wmb.45.2020.06.15.09.35.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 15 Jun 2020 09:35:05 -0700 (PDT) Subject: Re: [PATCH v2] spi: bcm2835: Enable shared interrupt support To: Mark Brown , Robin Murphy Cc: Florian Fainelli , lukas@wunner.de, "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" , "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" , Scott Branden , Ray Jui , linux-kernel@vger.kernel.org, "open list:SPI SUBSYSTEM" , Rob Herring , "maintainer:BROADCOM BCM281XX/BCM11XXX/BCM216XX ARM ARCHITE..." , "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" , Martin Sperl , Nicolas Saenz Julienne References: <20200604212819.715-1-f.fainelli@gmail.com> <142d48ae-2725-1368-3e11-658449662371@arm.com> <20200605132037.GF5413@sirena.org.uk> <2e371a32-fb52-03a2-82e4-5733d9f139cc@arm.com> <06342e88-e130-ad7a-9f97-94f09156f868@arm.com> <20200608112840.GC4593@sirena.org.uk> From: Florian Fainelli Message-ID: Date: Mon, 15 Jun 2020 09:34:58 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Firefox/68.0 Thunderbird/68.9.0 MIME-Version: 1.0 In-Reply-To: <20200608112840.GC4593@sirena.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 6/8/2020 4:28 AM, Mark Brown wrote: > On Mon, Jun 08, 2020 at 12:11:11PM +0100, Robin Murphy wrote: > >> Again, 2 cycles. The overhead of a static key alone is at least 50% of that. >> And that's not even considering whether the change in code layout caused by >> doubling up the IRQ handler might affect I-cache or branch predictor >> behaviour, where a single miss stands to more than wipe out any perceived >> saving. And all in code that has at least one obvious inefficiency left on >> the table either way. > >> This thread truly epitomises Knuth's "premature optimisation" quote... ;) > > In fairness the main reason this driver is so heavily tuned already (and > has lead to some really nice improvements in the core) is that there are > a number of users hitting 100% CPU utilization driving SPI devices on > some of the older RPi hardware, IIRC around IIO type applications > mostly. I do tend to agree that this particular optimization is a bit > marginal but there has been a lot of effort put into this. OK, so this has been dropped for spi/for-next right? How do we move from there? -- Florian