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=-6.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 47B1AC43465 for ; Mon, 21 Sep 2020 14:02:45 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 EB14F20756 for ; Mon, 21 Sep 2020 14:02:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="fRP032XT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org EB14F20756 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+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=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding: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=1SufTbmoFXXLNeer4fYB7vXDpndnaSevS9qkQag9qrM=; b=fRP032XTzuJB9kYGj3ajm/yx9 6xuvM97v1bODh1BlrkXQb1BjyRGZGtRLywg4YVefAcwHd5R+7+sb4hS8lG3c+M3tpwzJUB3McuQMI 3mCE3eFaifCtPIQU49c7wFRbjS/kBkEUeMm118IxgydgFkLRXn9I25ewN/fywwlMSZXpLsF4UeVsf J/1zM/i1dtLWqOCgzg6i3EcM7s849NuVrZrMhQ3lSrXtyxYcyISWfdTrMFaludtrHbNEUBavm0ESD VcSRriNQqiMfiBhF8tIoQj8xOvb01Y6S8i+eoPVm6G+XaJ5otPjWvrhs9pk5mXKai8oeQT0GS3tCK 0ctSjZapA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kKMNX-00071v-9Y; Mon, 21 Sep 2020 14:01:15 +0000 Received: from lhrrgout.huawei.com ([185.176.76.210] helo=huawei.com) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kKMNS-0006wa-AK for linux-arm-kernel@lists.infradead.org; Mon, 21 Sep 2020 14:01:11 +0000 Received: from lhreml724-chm.china.huawei.com (unknown [172.18.7.106]) by Forcepoint Email with ESMTP id C85C03125A0D1D39BC16; Mon, 21 Sep 2020 15:01:00 +0100 (IST) Received: from [127.0.0.1] (10.210.166.25) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.1913.5; Mon, 21 Sep 2020 15:01:00 +0100 Subject: Re: [PATCH v2 0/2] iommu/arm-smmu-v3: Improve cmdq lock efficiency To: Will Deacon References: <1598018062-175608-1-git-send-email-john.garry@huawei.com> <20200921134324.GK2139@willie-the-truck> From: John Garry Message-ID: Date: Mon, 21 Sep 2020 14:58:10 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.1.2 MIME-Version: 1.0 In-Reply-To: <20200921134324.GK2139@willie-the-truck> Content-Language: en-US X-Originating-IP: [10.210.166.25] X-ClientProxiedBy: lhreml701-chm.china.huawei.com (10.201.108.50) To lhreml724-chm.china.huawei.com (10.201.108.75) X-CFilter-Loop: Reflected X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200921_100110_480064_A8839047 X-CRM114-Status: GOOD ( 16.80 ) 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: maz@kernel.org, joro@8bytes.org, linuxarm@huawei.com, linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 21/09/2020 14:43, Will Deacon wrote: > On Fri, Aug 21, 2020 at 09:54:20PM +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 a lot of time once we start getting many >> CPUs contending - from experiment, for 64 CPUs contending the cmdq, >> success rate is ~ 1 in 12, which is poor, but not totally awful. >> >> This series removes that cmpxchg() and replaces with an atomic_add, >> same as how the actual cmdq deals with maintaining the prod pointer. > > I'm still not a fan of this. :( > Could you try to adapt the hacks I sent before, > please? I know they weren't quite right (I have no hardware to test on), but > the basic idea is to fall back to a spinlock if the cmpxchg() fails. The > queueing in the spinlock implementation should avoid the contention. OK, so if you're asking me to try this again, then I can do that, and see what it gives us. John _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel