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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,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 7095CC433DF for ; Thu, 16 Jul 2020 10:22:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4598720853 for ; Thu, 16 Jul 2020 10:22:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594894960; bh=vzEaE1HWTa7LYtbebB7ritpzkpel2YtikBtG3CEZDzU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=N/OULG3t9cADb2fWSUQ096Eu/PpWatxCyJ/7JmT1X8DcTT/X25T0LQ/OXC/THze/q TtwBiMYyw3djDshXEcrdp9a6iPGo8S4LHMDCSejGglfypGZmES9kJfEAm3dCtXt+CO zxH8xKYtTUJw8SUIb1bxN5dpDWLAyeD+u5Zc4v1Y= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726832AbgGPKWi (ORCPT ); Thu, 16 Jul 2020 06:22:38 -0400 Received: from mail.kernel.org ([198.145.29.99]:41458 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725996AbgGPKWi (ORCPT ); Thu, 16 Jul 2020 06:22:38 -0400 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 89A51204EA; Thu, 16 Jul 2020 10:22:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1594894958; bh=vzEaE1HWTa7LYtbebB7ritpzkpel2YtikBtG3CEZDzU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=O7qT433Bf508kbmPUyZtGJ1ha3eKm5yrmKHurnYxiVO1tk+RfIFdFzfIP9a4dEULJ cxskKb6f2hESv3IlEBT1RUtZQsbEm8i3bC2eetulC0gX+ABbte+A6hbUMZv5oMxo3Z dEeF7i7CvTyJM+Yn2p8YoEk1EHckrb6iEUSt+mB4= Date: Thu, 16 Jul 2020 11:22:33 +0100 From: Will Deacon To: John Garry Cc: robin.murphy@arm.com, joro@8bytes.org, trivial@kernel.org, linux-arm-kernel@lists.infradead.org, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, maz@kernel.org Subject: Re: [PATCH 0/4] iommu/arm-smmu-v3: Improve cmdq lock efficiency Message-ID: <20200716102233.GC7036@willie-the-truck> References: <1592846920-45338-1-git-send-email-john.garry@huawei.com> <20200716101940.GA7036@willie-the-truck> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200716101940.GA7036@willie-the-truck> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 16, 2020 at 11:19:41AM +0100, Will Deacon wrote: > On Tue, Jun 23, 2020 at 01:28:36AM +0800, John Garry wrote: > > As mentioned in [0], the CPU may consume many cycles processing > > arm_smmu_cmdq_issue_cmdlist(). One issue we find is the cmpxchg() loop to > > get space on the queue takes approx 25% of the cycles for this function. > > > > This series removes that cmpxchg(). > > How about something much simpler like the diff below? Ah, scratch that, I don't drop the lock if we fail the cas with it held. Let me hack it some more (I have no hardware so I can only build-test this). Will