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=-8.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 BD36BC433E1 for ; Thu, 16 Jul 2020 13:33:14 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (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 8F46920760 for ; Thu, 16 Jul 2020 13:33:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8F46920760 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 36C9E8A697; Thu, 16 Jul 2020 13:33:14 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id lObgKFI9NP1D; Thu, 16 Jul 2020 13:33:13 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id 44F038A477; Thu, 16 Jul 2020 13:33:13 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 1754EC0893; Thu, 16 Jul 2020 13:33:13 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) by lists.linuxfoundation.org (Postfix) with ESMTP id AA3E4C0733 for ; Thu, 16 Jul 2020 13:33:11 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 999398A641 for ; Thu, 16 Jul 2020 13:33:11 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id XZ-B7-p37Tw6 for ; Thu, 16 Jul 2020 13:33:09 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from huawei.com (lhrrgout.huawei.com [185.176.76.210]) by hemlock.osuosl.org (Postfix) with ESMTPS id 8C0318A477 for ; Thu, 16 Jul 2020 13:33:09 +0000 (UTC) Received: from lhreml724-chm.china.huawei.com (unknown [172.18.7.108]) by Forcepoint Email with ESMTP id 9F5A2950D01906284ED5; Thu, 16 Jul 2020 14:33:06 +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 14:33:05 +0100 Subject: Re: [PATCH 0/4] iommu/arm-smmu-v3: Improve cmdq lock efficiency To: 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: <54b0c8b9-d079-f832-2338-11cf6b09fa00@huawei.com> Date: Thu, 16 Jul 2020 14:31:17 +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: <20200716102814.GD7036@willie-the-truck> 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 Cc: trivial@kernel.org, maz@kernel.org, linux-kernel@vger.kernel.org, linuxarm@huawei.com, iommu@lists.linux-foundation.org, robin.murphy@arm.com, linux-arm-kernel@lists.infradead.org X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" 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... > > Will Unfortunately that hangs my machine during boot: [10.902893] 00:01: ttyS0 at MMIO 0x3f00003f8 (irq = 6, base_baud = 115200) is a 16550A [10.912048] SuperH (H)SCI(F) driver initialized [10.916811] msm_serial: driver initialized [10.921371] arm-smmu-v3 arm-smmu-v3.0.auto: option mask 0x0 [10.926946] arm-smmu-v3 arm-smmu-v3.0.auto: ias 48-bit, oas 48-bit (features 0x00000fef) [10.935374] arm-smmu-v3 arm-smmu-v3.0.auto: allocated 65536 entries for cmdq [10.942522] arm-smmu-v3 arm-smmu-v3.0.auto: allocated 32768 entries for evtq > > --->8 > > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c > index f578677a5c41..e6bcddd6ef69 100644 > --- a/drivers/iommu/arm-smmu-v3.c > +++ b/drivers/iommu/arm-smmu-v3.c > @@ -560,6 +560,7 @@ struct arm_smmu_cmdq { > atomic_long_t *valid_map; > atomic_t owner_prod; > atomic_t lock; > + spinlock_t slock; > }; > > struct arm_smmu_cmdq_batch { > @@ -1378,7 +1379,7 @@ static int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu, > u64 cmd_sync[CMDQ_ENT_DWORDS]; > u32 prod; > unsigned long flags; > - bool owner; > + bool owner, locked = false; > struct arm_smmu_cmdq *cmdq = &smmu->cmdq; > struct arm_smmu_ll_queue llq = { > .max_n_shift = cmdq->q.llq.max_n_shift, > @@ -1387,27 +1388,38 @@ static int arm_smmu_cmdq_issue_cmdlist(struct arm_smmu_device *smmu, > > /* 1. Allocate some space in the queue */ > local_irq_save(flags); > - llq.val = READ_ONCE(cmdq->q.llq.val); > do { > u64 old; > + llq.val = READ_ONCE(cmdq->q.llq.val); > > - while (!queue_has_space(&llq, n + sync)) { > + if (queue_has_space(&llq, n + sync)) > + goto try_cas; > + > + if (locked) > + spin_unlock(&cmdq->slock); > + > + do { > local_irq_restore(flags); > if (arm_smmu_cmdq_poll_until_not_full(smmu, &llq)) > dev_err_ratelimited(smmu->dev, "CMDQ timeout\n"); > local_irq_save(flags); > - } > + } while (!queue_has_space(&llq, n + sync)); > > +try_cas: > head.cons = llq.cons; > head.prod = queue_inc_prod_n(&llq, n + sync) | > CMDQ_PROD_OWNED_FLAG; > > old = cmpxchg_relaxed(&cmdq->q.llq.val, llq.val, head.val); > - if (old == llq.val) > + if (old != llq.val) Not sure why you changed this. And if I change it back, it seems that we could drop out of the loop with cmdq->slock held, so need to drop the lock also. I tried that and it stops my machine hanging. Let me know that was the intention, so I can test. Thanks, John > break; > > - llq.val = old; > + if (!locked) { > + spin_lock(&cmdq->slock); > + locked = true; > + } > } while (1); > + > owner = !(llq.prod & CMDQ_PROD_OWNED_FLAG); > head.prod &= ~CMDQ_PROD_OWNED_FLAG; > llq.prod &= ~CMDQ_PROD_OWNED_FLAG; > @@ -3192,6 +3204,7 @@ static int arm_smmu_cmdq_init(struct arm_smmu_device *smmu) > > atomic_set(&cmdq->owner_prod, 0); > atomic_set(&cmdq->lock, 0); > + spin_lock_init(&cmdq->slock); > > bitmap = (atomic_long_t *)bitmap_zalloc(nents, GFP_KERNEL); > if (!bitmap) { > . > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu