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=-5.5 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 0155CC433DF for ; Thu, 16 Jul 2020 11:33:58 +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 BE6942074B for ; Thu, 16 Jul 2020 11:33:57 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="E++cyFpf" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BE6942074B 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=ktHnPzFVOeLLBnK3diypQcr9Xv/067OdvepQoAB0S6s=; b=E++cyFpf3cq+u+lp8LmEZuYCJ lqax6QXm3MsaaDnZYZ7CJWBhPwuo/adj0xl4KIDqRP7nuCjDd6RoB8EXLTaqhodPgqBL7Ti/u6FpT 3UpI5w9kHlcvonf9atPekMJgymOGAUBBy8x2FMbZ7u2NF4pIIatbGwbAvzcV0QlZAref/cpMlWa5V rzZdspN/Lnw17OWe3y3BS3UGgz2jqChqyVGlFi52FjvfFqWk9N8j7ihvtglzm6oaHVk+rPGXuOgtg 2iOsodTyLF0+6uaZQb6z0PJurxosa4uVI1GGq5r7sekQjYtbE9of8TPATrOOed3tW0KkDLGE84AgC xOL3UkJ0Q==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jw27k-0003Vs-Gx; Thu, 16 Jul 2020 11:32:24 +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 1jw27h-0003VL-47 for linux-arm-kernel@lists.infradead.org; Thu, 16 Jul 2020 11:32:22 +0000 Received: from lhreml724-chm.china.huawei.com (unknown [172.18.7.106]) by Forcepoint Email with ESMTP id 2518E8DCE03CF4265438; Thu, 16 Jul 2020 12:32:19 +0100 (IST) Received: from [127.0.0.1] (10.210.168.254) by lhreml724-chm.china.huawei.com (10.201.108.75) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.1913.5; Thu, 16 Jul 2020 12:32:18 +0100 Subject: Re: [PATCH 0/4] iommu/arm-smmu-v3: Improve cmdq lock efficiency To: Robin Murphy , Will Deacon References: <1592846920-45338-1-git-send-email-john.garry@huawei.com> <20200716101940.GA7036@willie-the-truck> <20200716102233.GC7036@willie-the-truck> <20200716102814.GD7036@willie-the-truck> From: John Garry Message-ID: Date: Thu, 16 Jul 2020 12:30:30 +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: Content-Language: en-US X-Originating-IP: [10.210.168.254] X-ClientProxiedBy: lhreml714-chm.china.huawei.com (10.201.108.65) 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-20200716_073221_302051_4B3F2240 X-CRM114-Status: GOOD ( 14.84 ) 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: "trivial@kernel.org" , "maz@kernel.org" , "joro@8bytes.org" , Linuxarm , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "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 16/07/2020 12:22, Robin Murphy wrote: > On 2020-07-16 11:56, John Garry wrote: >> On 16/07/2020 11:28, Will Deacon wrote: >>> On Thu, Jul 16, 2020 at 11:22:33AM +0100, Will Deacon wrote: >>>> 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). >>> >>> Right, second attempt... >> >> I can try it, but if performance if not as good, then please check mine >> further (patch 4/4 specifically) - performance is really good, IMHO. > > Perhaps a silly question (I'm too engrossed in PMU world ATM to get > properly back up to speed on this), but couldn't this be done without > cmpxchg anyway? Instinctively it feels like instead of maintaining a > literal software copy of the prod value, we could resolve the "claim my > slot in the queue" part with atomic_fetch_add on a free-running 32-bit > "pseudo-prod" index, then whoever updates the hardware deals with the > truncation and wrap bit to convert it to an actual register value. > That's what mine does. But I also need to take care of cmdq locking and how we unconditionally provide space. Cheers, John _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel