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Fri, 11 Jun 2021 00:37:24 +0000 From: Krishna Reddy To: Robin Murphy , Sai Prakash Ranjan CC: "linux-arm-msm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , Will Deacon , "linux-arm-kernel@lists.infradead.org" , Thierry Reding Subject: RE: [PATCH] iommu/io-pgtable-arm: Optimize partial walk flush for large scatter-gather list Thread-Topic: [PATCH] iommu/io-pgtable-arm: Optimize partial walk flush for large scatter-gather list Thread-Index: AQHXXT84btg0466hEE2rkvq94oyuZasMBHAAgACy+QCAAD6WAIAAB6mAgAAg2ACAAAWcgIAAPESAgACQdxA= Date: Fri, 11 Jun 2021 00:37:24 +0000 Message-ID: References: <20210609145315.25750-1-saiprakash.ranjan@codeaurora.org> <35bfd245-45e2-8083-b620-330d6dbd7bd7@arm.com> <12067ffb8243b220cf03e83aaac3e823@codeaurora.org> <266f190e-99ae-9175-cf13-7a77730af389@arm.com> <61c69d23-324a-85d7-2458-dfff8df9280b@arm.com> In-Reply-To: <61c69d23-324a-85d7-2458-dfff8df9280b@arm.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: arm.com; 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Fri, 11 Jun 2021 00:37:24 +0000 From: Krishna Reddy To: Robin Murphy , Sai Prakash Ranjan Subject: RE: [PATCH] iommu/io-pgtable-arm: Optimize partial walk flush for large scatter-gather list Thread-Topic: [PATCH] iommu/io-pgtable-arm: Optimize partial walk flush for large scatter-gather list Thread-Index: AQHXXT84btg0466hEE2rkvq94oyuZasMBHAAgACy+QCAAD6WAIAAB6mAgAAg2ACAAAWcgIAAPESAgACQdxA= Date: Fri, 11 Jun 2021 00:37:24 +0000 Message-ID: References: <20210609145315.25750-1-saiprakash.ranjan@codeaurora.org> <35bfd245-45e2-8083-b620-330d6dbd7bd7@arm.com> <12067ffb8243b220cf03e83aaac3e823@codeaurora.org> <266f190e-99ae-9175-cf13-7a77730af389@arm.com> <61c69d23-324a-85d7-2458-dfff8df9280b@arm.com> In-Reply-To: <61c69d23-324a-85d7-2458-dfff8df9280b@arm.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: arm.com; dkim=none (message not signed) header.d=none;arm.com; dmarc=none action=none header.from=nvidia.com; x-originating-ip: [216.228.112.22] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: a9f980b3-1c9d-4733-7fed-08d92c71152d x-ms-traffictypediagnostic: BY5PR12MB4322: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:10000; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" > > No, the unmap latency is not just in some test case written, the issue > > is very real and we have workloads where camera is reporting frame > > drops because of this unmap latency in the order of 100s of milliseconds. > > And hardware team recommends using ASID based invalidations for > > anything larger than 128 TLB entries. So yes, we have taken note of > > impacts here before going this way and hence feel more inclined to > > make this qcom specific if required. Seems like the real issue here is not the unmap API latency. It should be the high number of back to back SMMU TLB invalidate register writes that is resulting in lower ISO BW to Camera and overflow. Isn't it? Even Tegra186 SoC has similar issue and HW team recommended to rate limit the number of back to back SMMU tlb invalidate registers writes. The subsequent Tegra194 SoC has a dedicated SMMU for ISO clients to avoid the impact of TLB invalidates from NISO clients on ISO BW. >> Thinking some more, I >> wonder if the Tegra folks might have an opinion to add here, given >> that their multiple-SMMU solution was seemingly about trying to get >> enough TLB and pagetable walk bandwidth in the first place? While it is good to reduce the number of tlb register writes, Flushing all TLB entries at context granularity arbitrarily can have negative impact on active traffic and BW. I don't have much data on possible impact at this point. Can the flushing at context granularity be made a quirk than performing it as default? -KR _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu 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=-4.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 4E0F8C48BDF for ; Fri, 11 Jun 2021 00:39:40 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 11E9D6128A for ; 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Fri, 11 Jun 2021 00:37:24 +0000 Received: from BY5PR12MB3764.namprd12.prod.outlook.com ([fe80::d05:4bca:ea51:15af]) by BY5PR12MB3764.namprd12.prod.outlook.com ([fe80::d05:4bca:ea51:15af%6]) with mapi id 15.20.4219.023; Fri, 11 Jun 2021 00:37:24 +0000 From: Krishna Reddy To: Robin Murphy , Sai Prakash Ranjan CC: "linux-arm-msm@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , Will Deacon , "linux-arm-kernel@lists.infradead.org" , Thierry Reding Subject: RE: [PATCH] iommu/io-pgtable-arm: Optimize partial walk flush for large scatter-gather list Thread-Topic: [PATCH] iommu/io-pgtable-arm: Optimize partial walk flush for large scatter-gather list Thread-Index: AQHXXT84btg0466hEE2rkvq94oyuZasMBHAAgACy+QCAAD6WAIAAB6mAgAAg2ACAAAWcgIAAPESAgACQdxA= Date: Fri, 11 Jun 2021 00:37:24 +0000 Message-ID: References: <20210609145315.25750-1-saiprakash.ranjan@codeaurora.org> <35bfd245-45e2-8083-b620-330d6dbd7bd7@arm.com> <12067ffb8243b220cf03e83aaac3e823@codeaurora.org> <266f190e-99ae-9175-cf13-7a77730af389@arm.com> <61c69d23-324a-85d7-2458-dfff8df9280b@arm.com> In-Reply-To: <61c69d23-324a-85d7-2458-dfff8df9280b@arm.com> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: arm.com; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org > > No, the unmap latency is not just in some test case written, the issue > > is very real and we have workloads where camera is reporting frame > > drops because of this unmap latency in the order of 100s of milliseconds. > > And hardware team recommends using ASID based invalidations for > > anything larger than 128 TLB entries. So yes, we have taken note of > > impacts here before going this way and hence feel more inclined to > > make this qcom specific if required. Seems like the real issue here is not the unmap API latency. It should be the high number of back to back SMMU TLB invalidate register writes that is resulting in lower ISO BW to Camera and overflow. Isn't it? Even Tegra186 SoC has similar issue and HW team recommended to rate limit the number of back to back SMMU tlb invalidate registers writes. The subsequent Tegra194 SoC has a dedicated SMMU for ISO clients to avoid the impact of TLB invalidates from NISO clients on ISO BW. >> Thinking some more, I >> wonder if the Tegra folks might have an opinion to add here, given >> that their multiple-SMMU solution was seemingly about trying to get >> enough TLB and pagetable walk bandwidth in the first place? While it is good to reduce the number of tlb register writes, Flushing all TLB entries at context granularity arbitrarily can have negative impact on active traffic and BW. I don't have much data on possible impact at this point. Can the flushing at context granularity be made a quirk than performing it as default? -KR _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel